Just one of the several really big reasons why he can't afford to admit to it. Confessing to the account being his, is tantamount to confessing that he has been lying every single time he asserted he didn't have time to do X, and the one thing Phil has not ever copped to, to anyone, ever, is being a liar. He'll tell Katherine he was drinking a lot (I'm sure he was), he'll tell the camera he used to be really immature (glossing over the part where he still is), he'll acknowledge things he hates acknowledging but can't get away with memory-holding (like The Incident, because Keemstar made that shit go viral), he'll tell Rambo over the phone that he's really insecure while thinking that will stay between them, but he'll never admit that he has told so many huge lies.
Phil may not know much, but he knows how full of shit he is, and that giving it up means huge consequences.