You can read Phaedo online in English at the Perseus Project and in French at Wikisource.
The Characters: The Frame Narrative
Little is known of Echecrates, but there is a later tradition in which an Echecrates was among the last serious Pythagorean philosophers, and since Pythagorean ideas permeate this dialogue, it is likely the same person.
Phaedo of Elis
According to a later legend, Phaedo came to Socrates' attention because he was being sold as a slave, probably as a prisoner of war captured in Sparta's war against Elis a couple of years before. Socrates insisted that Crito buy him and set him free, and Crito did; but some versions of it say that it was Cebes rather than Crito (we have no way of knowing if this is presupposed by this dialogue, or if the dialogue is a reason why Cebes is sometimes part of the story). He is almost certainly the youngest person in the scene. He would go on to found a philosophical school at Elea and write dialogues, but none of the dialogues have survived even in fragments and nothing is known about what he taught at his school. A later legend says that there was a rivalry between Plato and Phaedo, and that Phaedo accused Plato of misrepresenting his views, but there are later legends about Plato having rivalries with almost anyone else who founded a philosophical school, so it is difficult to know what to make of any of them.
The Characters: In the Prison
Phaedo divides the students and friends actually present according to their cities. There are Athenians (Apollodorus, Critobulus, Crito, Hermogenes, Epiganes, Aeschines, Antisthenes, Ctesippus, Menexenus, and some others including Phaedo himself), Thebans (Simmias, Cebes, Phaedonides), and Megarans (Euclides, Terpsion). Note that the two cities besides Athens noted as especially well governed in Crito are Thebes and Megara. Also, most, although not all, of the people in attendance would go on to write Socratic dialogues.
[Three students are explicitly noted as absent: Plato (who is sick), and Aristippus and Cleombrotus (who are both away at Aegina). Later gossip, recorded by Diogenes Laertius, claimed that Aristippus actually was there, but was written out of the scene by Plato, who hated him. Almost the only thing we know about Cleombrotus is that a legend grew up, based on something written by Callimachus, saying that he committed suicide on reading this very dialogue, for reasons never made entirely clear -- at least, assuming that it is the same Cleombrotus, since the name was not uncommon. (Xenophon, it should be noted, is in exile. But perhaps he is represented by proxy through Hermogenes?)]
The speaking parts are:
The first to speak in the prison are the guard and Xanthippe, Socrates' wife, who is there with their son.
Cebes of Thebes
Cebes is said here to be a student of Philolaus, the Pythagorean philosopher. Xenophon also depicts him as in the circle of Socrates, in the episode with Theodote in Memorabilia. There is a famous work, the Tablet of Cebes, that was attributed to him in antiquity and is still extant
Simmias of Thebes
Simmias is also a student of Philolaus, and Xenophon also identifies him as being in the circle of Socrates. In Phaedrus he is said to like arguments more than anyone else Socrates knows.
Phaedo of Elis
There is also an officer of the Eleven, in charge of making sure the law is followed properly.
The Plot and The Thought
Echecrates opens the dialogue by asking Phaedo questions about Socrates' death; Phaedo notes that he was there himself and explains why Socrates was not executed immediately after his trial. He agrees to tell Echecrates the details, noting that it was a strange experience. Although he was witnessing the death of a friend, he did not pity Socrates; but as they engaged in philosophical discussion, he felt a strange mixture of pleasure and pain, as they all did.
They arrived at the prison on the day, early before dawn. They had developed a routine of visiting Socrates, and would gather outside before the guard let them into his room, which was usually quite late. But the evening before they had been told that the ship had arrived from Delos, so on that day they were as early as possible. When they arrive, the official for the Eleven is releasing Socrates from his chains and explaining the process. They enter and find Xanthippe there with their little boy on her knees. On seeing them, she cries out with "the sort of thing that women usually say" (60a) and Socrates has Crito have some of his people take her home. (One of the things the dialogue will expressly signal at the end is that, as the end draws near, all the male friends are themselves having difficulty not saying "the sort of thing that women usually say", so there's a bit more going on here than the usual ancient Greek misogyny.)
Socrates sits up and rubs his legs, remarking that the relation between pleasure and pain is curious; you cannot exactly have both at the same time, but they seem joined together:
I think that if Aesop had noted this he would have composed a fable that a god wished to reconcile their opposition but could not do so, so he joined their two heads together, and therefore when a man has the one, the other follows later. (60c)
Note the fact that this point has been stated twice just a few pages into the dialogue, both in the frame narrative and in the narrative within the frame.
Cebes remarks that this reminds him that he was talking with Evenus the poet, and had been asked why Socrates, who never wrote poetry, to start putting the poems of Aesop into verse and to compose a hymn to Apollo. Socrates replies that heis doing it because of certain dreams he has always had. He would often have a dream with the message that he should practice what pertains to the Muses (musike). He had always taken this to mean that he should continue doing as he had been doing, practicing philosophy, "the highest kind of art" (61a), but after the trial while waiting in prison because of the god Apollo's festival, it occurred to him that he had better cover all his bases, just in case the dream actually meant that he was to practice music in the popular sense. Thus he set out to write poetry, starting with the hymn to Apollo. Then it occurred to him that the thing that is to poets what argument is to philosophers is story, so he began versifying the stories he had on hand, which happened to be various fables of Aesop. He then ends;
Tell this to Evenus, Cebes, wish him well and bid him farewell, and tell him, if he is wise, to follow me as soon as possible. (61b)
Simmias remarks that Evenus probably would not want to do so, and Socrates remarks that if he is a philosopher, he would be willing to do so, although, indeed, it is perhaps not right to take one's own life. (As if to mark this as important, Phaedo notes that Socrates at this put his feet on the ground so that he was sitting, not lying, and remained this way for the rest of the discussion.)
Cebes asks what he means by this, because it is somewhat strange to say that we should welcome our deaths and yet not hasten them. So Socrates begins his explanation with what seems to be an allusion to Crito, saying that one account is "that we men are in a kind of prison, and that one must not free oneself or run away" (62b). However, he goes on to say that the account seems appropriate that holds that we are possessions of the gods, who are our guardians, and that we must not kill ourselves before the gods indicate that it is necessary. But Cebes turns this around and says that it seems unreasonable, if that is so, for anyone not to resent leaving the service of the god, so it is wiser not to want to die.
Socrates likes this argument, but replies that he does not resent it because he thinks he will in fact go to "other wise and good gods, and then to men who have died and are better than men here" (63b), although he does not insist on the latter, only on the former. It's very important to see that this is the set-up for all the discussion of immortality: Socrates will be arguing in particular that on death we do not leave the service of the gods, but continue, and if we have prepared ourselves properly for the state we will be in, we will have more of a share in divine things than we do in this life through philosophy and virtue.
Socrates notes that "the one aim of those who practice philosophy in the proper manner is to practice for dying and death" (64a). Death is separation from the body, but philosophy, too, is separation from the body. The philosopher must rise above the bodily character of pleasures and pains (note that they come up again) and go beyond the potentially misleading information of the senses. The senses do not provide us any direct grasp of the just, the beautiful, the good, or anything like this; in order to understand these things we must go beyond the senses, and think them through purely intellectually, at least as much as possible. The body drags us down with distractions, both distractions keeping us from knowledge and distractions keeping us from virtue; philosophy is a discipline of not being bogged down by this. Thus we see that "if we are ever to have pure knowledge, we must escape from the body and observe things in themselves with the soul by itself" (66e). Thus philosophy is in reality a state of life in which one tries, as far as possible, to live so that one's soul is separated from one's body; but separation of soul and body is death. Thus "those who practice philosophy in the right way are training for dying and they fear death least of all men" (67e). Anyone who is resentful of death is not a lover of wisdom (philosopher) but a lover of body or bodily things. And we see this with fortitude and temperance as well as with prudence: those who have these virtues rise above bodily things like pleasure and pain: "moderation and courage and justice are a purging away of all such tihngs, and wisdom itself is a kind of cleansing or purification" (69b-c).
Cebes remarks that this is all quite excellent, but that most people will have difficulty believing it, because they will have difficulty believing that the soul survives death and still possesses reason and ability. So is there reason to think that souls continue to exist in the underworld? Socrates remarks that if we look at the whole of nature, we find that opposites come from opposites. The opposites he has in mind here are comparative oppositions: larger-smaller, stronger-weaker, and so forth, these things in which a smooth transition from contrary to contrary is possible. It may seem odd to think of living-dead as one of these, but recall that we just finished recognizing death as separation of body and soul, and the recognition that philosophy is also such very clear requires us to recognize separation of body and soul as a sort of sliding scale allowing precisely this kind of smooth transition. Thus more alive comes from more dead and more dead from more alive. Thus it seems that the living can come from the dead, and thus that there are enduring souls of the dead.
Cebes jumps in and notes that this seems to fit what Socrates has said before about recollection. (It seems often forgotten by commentators that it is Cebes, not Socrates, who brings up this argument at this point.) The dialogue here alludes to the argument of Meno: we are capable of learning because learning is like being reminded of what we already knew when we came into the world. Socrates explains the doctrine of recollection (since we don't get the idea of the equal from the senses, we must already have acquired it, but we need to be reminded of it). Thus it seems that we existed before we were born. Simmias notes that this does not seem to establish that we continue to exist after we die, but Socrates returns the discussion to the previous argument about contraries.
Socrates jokes that they seem to think that the soul disperses at death, especially if there is a high wind, but points out that things that disperse or scatter are composite. The equal, or the beautiful, or the just are all things that remain the same, and they are things that can only be properly grasped by intellect, not by senses; but we have body and soul, and our soul, too, is known in the same way that the beautiful itself and the equal itself are known, and, moreover, we have alrady seen in the discussion of philosophy that for the soul to fully live a life of wisdom and virtue, it must rise above the things of the body. When it has wisdom and virtue it becomes even more like the beautiful itself, remaining the same rather than straying through distractions. We recognize that the body is mortal because it has all the properties indicating that it dissolves easily; but since the soul has properties that make it more similar to "the divine, deathless, intelligible, uniform, indissoluble, always the same as itself" (80b), one would expect it to be indissoluble. A philosophical soul has been training to be more like these indissoluble things, and has taken on something of the purity and stability of them; so what reason could one have for taking it to dissolve with the body? In other words: the fact that philosophy is separation of soul and body indicates that the soul survives the separation of soul and body that is death; death is just a continuance of what philosophy is in life, and the soul of the philosopher is already trained and prepared for it.
After some discussion of this, Socrates falls silent for a long time. Cebes and Simmias start whispering, though, and Socrates asks them whether they think the argument is missing something important. Simmias replies that he and Cebes do have some difficulty, but were hesitant to bother Socrates with it in his misfortune. Socrates remarks drily that the two Thebans must think him less of a prophet than the swans, which sing beautifully just before they die because "they rejoice that they are about to depart to join the god whose servants they are" (85a). Since Socrates, like the swans, is dedicated to the god Apollo, he has received a gift of prophecy like theirs and so is no more sorrowful to leave life than they are. (Note, incidentally, the implied link between Socrates and music again.)
Simmias suggests a problem for Socrates' argument by introducing the Pythagorean idea of the soul as a harmony of the body. It seems that one could run a parallel to Socrates' argument using harmony: "a harmony is something invisible, without body, beautiful and divine in the attuned lyre, whereas the lyre itself and its strings are physical, bodily, composite, earthy and akin to what is mortal" (85e-86a). Thus someone could argue that if the lyre is destroyed, the harmony must still exist. On the other hand, if the soul is a harmony of the body, it seems it must be destroyed as soon as the lyre is destroyed, regardless of how divine it might be.
Cebes suggests a different problem. While he accepts the argument from recollection that the soul existed before the body, and does not agree with Simmias's objection because a soul seems stronger than the body, nonetheless it seems that the soul could wear out many bodies and yet still not survive the last of them, just as a man could wear out many cloaks and yet still have a cloak that outlasts him. Perhaps the soul can indeed survive the death of the body, but is worn out or harmed at each birth and death, until it is itself finally destroyed.
Phaedo says that on hearing these objections, everyone (except Socrates) became depressed, because they had been carried along by Socrates' argument, but these seemed to them to show that this was a subject on which perhaps no one could know anything; and at this point (88c) the frame narrative breaks in again.
* Socrates directly refers to Aristophanes' The Clouds at 70c (cp. Apology).
* We've seen the idea elsewhere that philosophy is under the province of the Muses (Phaedrus), the Muses Calliope and Urania, in particular; and as noted there, Plato's own Academy was technically a religious institution devoted to the Muses.
* By alluding to the argument in the Crito, this dialogues deepens the implications of that dialogue, by showing that its argument, mutatis mutandis, applies not just to Socrates in prison but also to the philosopher in life.
* As noted above, Socrates places no real weight on the argument from recollection at this point; he explains recollection, but it is Cebes who repeatedly emphasizes it. In Meno, Socrates says the idea is based on things he has heard from those who say the soul is immortal, so it may well be that he thinks using it would be circular. People sometimes try to suggest an opposition between this argument and Socrates' comments about philosophy as a separation from body by noting that recollection is understood in terms of sense experiences reminding us of the intelligible, thus giving the senses a role in cognition; but the attempt to turn this into an opposition strikes me as remarkably implausible, since it assumes that recollection of the equal and understanding of the equal are the same, which they manifestly are not. In addition, it cannot explain why Socrates goes on to reaffirm what seems to be the same idea of philosophy.