We can try to make all the justifications as to how this could be fake, but I think that the nail in this coffin ironically came when it was first found. I can think of multiple ways that Phil could have faked it at the start that would have created enough doubt to keep us running in circles. He could have said that he was an old fan who copied the name, he could have claimed to be a "troll", and, if I was telling him what to say, he should have said that he was a fan or just some nobody who bought Phil's account after Phil realized how much he'd been sucked in and Kat snapping him out of it. Phil even could have brought it up on stream when someone confronted him the next day. He could have "admit" to spending a few hundred to a couple thousand in mobile games like this when he was depressed, tell the paypigs an inspiring story of how your soulmate made you realize how bad things were, implicitly blame Leanna without saying her name and tell them how you made a responsible financial decision and sold it to get your money back. Brag about how you actually made money if you want to go full Phil. Tell them you never mentioned it before because it was a private issue, you were a little ashamed, "and you guys know I don't like to talk about my behind the scenes financial shit if I don't have to. We're here to game and be positive, dood!" We'd all smell a rat immediately but what could we honestly do to disprove that? Every new purchase would have a ready made explanation and we'd be the bad guys for harassing some random dude online.
But he had to pretend he had no idea who the streamer DSP was, how this was all a coincidence and then deny it on stream. That one split second, dumb lie which is so Phil doomed him so every piece of evidence only made it more and more obvious who it really was.
Best of all, if he had literally one IRL friend, he could have killed this by taking a picture of them with a piece of paper saying they were "TheyCallMeDSP" and sending it to his guild day one. No one there would have cared after that: they'd have their plausible deniability and they'd happily keep taking his cash. This is the perfect DSP story because it encompasses everything about Phil and why he is his own worst enemy.