I don't remember the exact timeline, but Phil used to complain about how predatory mobile games were. At the time, it seemed like the general reasonable assumptions that even someone as dumb as Phil would make just from an outsider's perspective, and there was still a great deal of debate over what Phil was actually doing on his money so I don't remember anyone saying even Phil is that dumb to be a whale. And to their credit, they were probably right, I suspect he's been hooked on mobile games for awhile and I believe there's been a few deep dives into old games to find older accounts and they didn't seem particularly whaled out.
I'm guessing like most addictions, it started pretty small and it really spiraled by the time that Phil got into Champions. It probably helped that it was a game about one of Phil's other big interests, wrestling. There's a lot of nostalgia bait there, and Phil normally falls for that. Phil probably got more absorbed too as he became more of a hermit. One of the few things he genuinely seems to enjoy, as much as Phil can, is being a consumer, so getting to spend without leaving his home is basically his dream.