Based on a great conversation I had with @leonawriter.
So I headcanon that the truth and bringing about justice have always been important to Phoenix ever since the class trial. But he was a) never aware of it because his self-awareness sucks, and b) defending the innocent took priority because it aligns more with his personal nature.
He wants to follow Miles and his new-found credo about finding the truth since case 2-4 / Farewell My Turnabout. He wants to. He admires Miles and his pursuit of truth because he recognizes on some level this is pivotal.
But it doesn’t come naturally to him like pursuing justice comes to Apollo. His first instinct is to protect people due to his experiences with the class trial and Dahlia, with specific bias to these who he feels resemble himself in some way.
Also - his view on what ‘truth’ is has become severely distorted.
An authority figure, a teacher who’s a big thing to a 9-year-old child, accused him with the rest of the class of stealing when he had not done it. Who’s to say there weren’t any nasty rumors circulating at Phoenix’s school after the class trial? That some kids and teachers still believed he had stolen Miles’ lunch money?
Phoenix slipped into a similar situation like the class trial in college where nobody believed in his innocence in regards to Doug Swallow’s murder, where he discovers ‘Dollie’ never loved him, lied to him. And rumors could have started again - just more vicious because a murder happened.
Now imagine Phoenix meeting Miles, who was one of the two people who defended him in the class trial, tearing into him about murdering Mia.
And Miles said in the same game, in the context of his own self-hatred, trauma,
and belief he had killed his father, ‘I
believe everybody is guilty of something.’
It must have felt like the deepest betrayal to Phoenix, even with the later realization about why Miles was talking like this. He compounded a belief that has been festering inside his friend’s mind for years.
I’ll use a quote from one of @leonawriter‘s meta posts about the class trial:
'Unless somebody speaks up for you, nobody is going to believe you when you’re innocent. And sometimes they don’t even believe you then.’
Phoenix has a fundamental doubt that the truth is going to matter, because people will always believe what they want to believe. People don’t want to think or check their beliefs. Society likes easy lies and scapegoats so it can return to the status-quo. The entire police system is corrupted under Damon Gant. Or, If I find the truth, people will believe the prosecutor, not me. Or in the Engard trial, If I’ll tell the truth, Maya will die!
Or, if you also count PLvsAA as canon, I found the truth that Maya isn’t a witch yet she was still cast into the fire! She died! I did my best but it wasn’t enough.
That’s what his experiences as a lawyer so far have told him.
He needs prosecutors like Miles who push him into the right direction. He needs people he can trust to motivate him to find the truth - but who knows if they won’t turn on him like Dahlia or his classmates did?
He still wants to pursue the truth- but this conflicts with the other parts of his internal belief (and doubt) system. The seeds were there before, but it broke out due to the events during Farewell My Turnabout. It wasn’t even resolved in Bridge to the Turnabout because the games don’t acknowledge it.
I can imagine it to be canon that he could have broken, once (not with AA4 in mind here) when facing another disaster like the ones I mentioned after T&T, and ranted how utterly useless and pointless it is to find the truth. He knows deep down it’s not true but he’s just so tired and disappointed…