No chance, imo. With Phil's impulse control and access to easy money, any addiction he picked up would be pretty evident to us, if not at the very least because Phil has access to the amounts of money that would easily buy him an OD if it was drugs. At most we've only ever seen him possibly drunk on camera, and heard stories about him smoking weed that imply he's never been in the same room as weed, let alone anything stronger. I think you underestimate just how much a whale in the throes of a song can spend, and just how exploitative the game(s) he chose to whale on can be.
tl;dr Addiction to drugs or gambling: it still triggers the same part of the brain, so we can see a lot of the same psychological effects of addiction, but we don't have any other physiological signs of a drug habit besides booze, and Phil is not the image of a full-on boozehound, or we'd have way better streams.