I'll summarize the case about the Phaedo, and then in another post say what I think is really at issue (no, we haven't yet touched upon it, I believe!).
1. Plato is usually articulating ideals. So perhaps his talk of 'true philosophers' is to be understood in an implicitly reduplicated sense. I.e. "Only true philosophers have virtue" = "A person has virtue only insofar as he is a philosopher." How can this be ruled out? I don't see that it can.
2. The Phaedo clearly affirms that it is possible to grasp the Forms and attain to virtue in various degrees--(perhaps only among philosophers, but the principle of the thing is acknowledged).
3. Plato is happy, at times, to talk in an ordinary way, as if goodness and badness are widely distributed among people.
4. Non-philosophers differ, if not in virtue, then in something that is like virtue, and which provides a basis for differences in rewards and punishments after death.
As regards 3. , think also of the famous 'misology' passage. Misology is
a shameful state of affairs...and obviously due to an attempt to have human relations without any skill in human affairs, for such skill would lead one to believe, what is in fact true, that the very good and very wicked are both quite rare, and that most men are between these extremes (Grube, 89e-90a).
...ai)sxro/n, kai\ dh=lon o(/ti a)/neu te/xnhj th=j peri\ ta)nqrw/peia o( toiou=toj xrh=sqai e)pexei/rei toi=j a)nqrw/poij; ei) ga/r pou meta\ te/xnhj e)xrh=to, w(/sper e)/xei ou(/twj a)\n h(gh/sato, tou\j me\n xrhstou\j kai\ ponhrou\j sfo/dra o)li/gouj ei)=nai e(kate/rouj, tou\j de\ metacu\ plei/stouj.
Most of us are 'in between' (metaxu) ! And this passage occurs immediately after those that we have been looking at, where Socrates seems to say that only philosophers can be virtuous!
But, as I said, I don't think that even this touches upon the key point.