To be fair, Phoenix wasn't exactly immune to the idiot ball in his first game either. For three cases in a row he thought it would be a good idea to confront a suspected murderer with evidence of their misdeeds outside of the courtroom.
Well maybe he didn't think von Karma was a murderer yet, but he was definitely not trustworthy.
It's tempting to linger in this moment, while every possibility still exists. But unless collapsed by an observer, they will never be more than possibilities.