I'm not sure I can do it justice in an adhoc way, but it's important to keep in mind there are a few layers of irony that the piece is working on. First, Socrates, who does not write, is being presented as a character, in written form, by his disciple. So obviously Plato does not share Socrates' views on writing, even if he finds them interesting and valuable.

Second, in the dialogue, there are a bunch of examples of texts that are presented by the characters: the speech from Lysias, which Phaedrus has hidden in his cloak, then the speech from Socrates, that he disavows, then another speech, taking the opposite position. There's also the (fascinating) recounting of a legend about Thoth, and the invention of writing, which plays on the fact that the greek word for 'medicine' is the same as that for 'poison'.

It's a really rich text - as, I guess, you might expect from a really brilliant writer who was also a disciple of a philosopher who never wrote a word. I tend to think of it as a serious attempt to describe the conceptual differences between speech and writing - something people tend to collapse ('writing is recorded speech', etc).