The story goes that Thamus said many things to Theuth in praise or blame of the various arts, which it would take too long to repeat; but when they came to the letters, “This invention, O king,” said Theuth, “will make the Egyptians wiser and will improve their memories; for it is an elixir of memory and wisdom that I have discovered.”
(The word for 'elixir' here is pharmakon, the closest translation of which is perhaps 'drug'; like the English word, it can mean something medicinal or something poisonous.)
But Thamus replied, “Most ingenious Theuth, one man has the ability to beget arts, but the ability to judge of their usefulness or harmfulness to their users belongs to another; and now you, who are the father of letters, have been led by your affection to ascribe to them a power the opposite of that which they really possess. For this invention will produce forgetfulness in the minds of those who learn to use it, because they will not practice their memory. Their trust in writing, produced by external characters which are no part of themselves, will discourage the use of their own memory within them. You have invented an elixir [pharmakon] not of memory, but of reminding; and you offer your pupils the appearance of wisdom, not true wisdom, for they will read many things without instruction and will therefore seem to know many things, when they are for the most part ignorant and hard to get along with, since they are not wise, but only appear wise."
Writing is a drug that promises much but also creates addictive dependencies!
Phaedrus says to Socrates that he's very good at making up stories from Egypt; to which Socrates replies that in ancient times, when people weren't as wise as young whippersnappers today, people were content to listen to even a rock or a tree if only it told the truth. Phaedrus accepts the teasing rebuke, and agrees with Thamus; at which point Socrates notes that if Thamus is right, the only use of writing is to remind people of what they already know.
He then goes on to say that written logos (=reason/word/speech) has the curious characteristic that, if done well, it seems to be intelligent, but it only ever says the same thing, over and over again. It does not clarify itself, it does not answer questions put to it, it does not defend itself. It is a bastard logos, whose legitimate brother is the living, breathing logos of one who knows; the written logos is only an image of this one in the same way that a portrait painting is only an image of a real person.
If you are planting a garden of Adonis, you do it for play and festivity; if you really wish a harvest, you follow the rules of farming, find appropriate soil, and prepare to wait for eight months. But surely someone who knows what is just, what is good, and what is beautiful, will have as much sense about his logoi as a farmer about his seeds:
The gardens of letters he will, it seems, plant for amusement, and will write, when he writes, to treasure up reminders for himself, when he comes to the forgetfulness of old age, and for others who follow the same path, and he will be pleased when he sees them putting forth tender leaves. When others engage in other amusements, refreshing themselves with banquets and kindred entertainments, he will pass the time in such pleasures as I have suggested. (276d)
Phadrus does note that telling stories about justice in this way is a noble way to pass the time, and Socrates agrees, but insists that serious discourse is even better, in which one uses the method of dialectic to plant intelligent logoi in the soul of another which can then bear fruit in others. Written words by their very nature are something playful, and the best and most serious purpose they can serve is to remind us of what we already know. But the person who knows about justice and the like has words of true value, and deserves to be called a lover of wisdom or, which is to say the same thing -- philosopher. Socrates then ends with a prayer to the gods of the place for beauty within.
* Gardens of Adonis were a common part of the Adonia festival in July. Seeds would be planted in very shallow containers, and women would tend them for eight days. The plants would grow rapidly but have very little in the way of roots. Then, at the end of the eight days, they would take the plants and smash them or throw them into the ocean. Saying that something was a garden of Adonis in ancient Greece was the same as saying that it was sterile, superficial, and had no further value. It's worth noting that Adonis was a favorite of Aphrodite and the Adonia was an erotically themed festival celebrated entirely privately.
* It's possible to overdo one's interpretation of the criticism of writing here. Both Socrates and Phaedrus are looking specifically at the question of what kind of writing is good writing, and this requires looking at what writing can do. The fact that writing can only remind people of what they know is not unique to writing, as one can see by reading Meno, so that writing does this is not itself a criticism but, in fact, a noble thing. The weakness of writing is not that it is a reminder but that any kind of writing is on its own a kind of ritual festivity, good for a holiday, but only able to work in a very superficial way. Serious teaching requires a level of defense, question, adaptation, that writing can never yield.
* People often have difficulties grasping the unity of the dialogue, so it should be pointed out that the Myth of Theuth is not merely tacked on to the rest of the dialogue, nor is it entirely concerned with a different subject than the parts of the dialogue that concern love. We have two clear signs of this: the reference to the gardens of Adonis to describe writing and the application of the title 'philosopher' to those who use serious discourse. Further, it is clear on a little thought that there is a strong parallel between the discussion of eros and the discussion of logos: Lysias's advice to the beloved is a written logos in which eros turns out to be as superficial and sterile in the same way as writing itself is, whereas Socrates's second speech is a living, breathing logos in which eros is made a matter of living, breathing souls, the way true teaching is.
And the dialogue itself is, of course, a written logos, put forward playfully to remind you of what you already know about eros.
All quotations are from Harold N. Fowler's translation at the Perseus Project.