There's an irony to people repeating this claim without even having read the Phaedrus. If they had, they'd understand that the concern with writing was that it was not able to respond as a human in dialogue. One could think that LLMs are an improvement in this regard, but for the fact that LLMs are actually autonomous sophists.

Socrates would have been against LLMs, and for good reason. Writing isn't unequivocally bad, but it is simply not a substitution for real dialogue and thought. We use books as a means by which to have more things to discuss with humans. LLMs can supplant the desire to even have dialogue with others, which is perhaps the more insidious thing.