Isn’t the language of the Phaedo generally that of approximation to an ideal? Socrates regards the philosophical life as a successive purification; he says that souls differ in how 'corporeal' they are; he describes a philosopher as someone who lives 'as much as possible' detached from the body. You can't become more purified, less corporeal, or more detached, if you weren't less so earlier.
Moreover, the entire scheme of reincarnation seems to presuppose variation in degree of virtue. To be sure, true philosophers are set apart: they’ve attained the ideal and, upon death, manage to escape cycles of reincarnation and become united with the gods. But everyone else becomes reincarnated within a hierarchy of animals, depending, it seems, upon the goodness of their lives. What could determine ranking here, except approximation to virtue and thus (in some sense) degree of virtue? If all non-philosophers were not virtuous and had only shadow virtues, how could they be ranked?
This question becomes pointed if we consider Phaedo 113d, precisely where Socrates describes judgment in the afterlife for 'average' (me/swj) people:
When the dead arrive at the place to which each has been led by his guardian spirit, they are first judged as to whether they have led a good and pious life. Those who have lived an average life make their way to the Acheron and embark upon such vessels as there are for them and proceed to the lake. There they dwell and are purified by penalties for any wrongdoing they may have committed; they are also suitably rewarded for their good deeds as each deserves (Grube).
e)peida\n a)fi/kwntai oi( teteleuthko/tej ei)j to\n to/pon oi(= o( dai/mwn e(/kaston komi/zei, prw=ton me\n diedika/santo oi(/ te kalw=j kai\ o(si/wj biw/santej kai\ oi( mh/. kai\ oi(\ me\n a)\n do/cwsi me/swj bebiwke/nai, poreuqe/ntej e)pi\ to\n )Axe/ronta, a)naba/ntej a(\ dh\ au)toi=j o)xh/mata/ e)stin, e)pi\ tou/twn a)fiknou=ntai ei)j th\n li/mnhn, kai\ e)kei= oi)kou=si/ te kai\ kaqairo/menoi tw=n te a)dikhma/twn dido/ntej di/kaj a)polu/ontai, ei)/ ti/j ti h)di/khken, tw=n te eu)ergesiw=n tima\j fe/rontai kata\ th\n a)ci/an e(/kastoj:
It’s the ‘being suitably rewarded’ which suggests degree of virtue. If non-philosophers were entirely non-virtuous, because they lacked the requisite perception of the Forms, then how could they do meritorious good deeds at all? (Rowe in his commentary says that the passage seems to suggest ‘some kind of hierarchy’ among the inhabitants of Hades, that is, degrees of virtue.)
A similar problem is raised by Plato’s saying next (113e2) that especially bad people are given special punishments because of ‘the enormity of their crimes’ (dia\ ta\ mege/qh tw=n a(marthma/twn). If all non-philosophers were not virtuous, because all of them lack the requisite perception of the Forms, then it’s hard to see how some of them could be especially bad.
The relevance of this is the following. If Plato in the Phaedo thinks that only philosophers can be virtuous in a strict sense, but others can have various degrees of virtue, in some looser sense, then he could easily hold that strict virtue alone is important for 'salvation' (the topic of the Phaedo), but that virtue in some approximating sense, too, is important for political theory.
It’s in the spirit of Dissoi Blogoi to counterpose arguments on a question. So in a subsequent post I’ll give Bobonich’s arguments against this, that the difference between virtue and non-virtue in the Phaedo is indeed all-or-nothing.
(Btw, Phaedo 113d-e is not discussed in Plato's Utopia Recast, although the book does comment on other eschatological passages in the dialogue.)