He was a patron as of last year (long after his disappearance) and asking Phil via Patreon questions about his schedule so he could book time off work to watch him.
Jeff was doxed after the Jasper stream when he dropped a large sum, causing his employer to hide their twitter due to the spam. Phil has since moved away from marathons with large goals that created the openings for Jeff to apparently tell him he was going to turn up to play a hero. The vest streak meant that every day became a self-contained goal that had to be maintained - which was Jeff's wheelhouse.
This move to OMM and the scheduled tips fixes every problem. Jeff can now watch Phil whenever and still support him, he can have his secret little gay relationship with his favorite parasite streamer while also not being publicly active and visible to make himself a target for the trolls, and he can own the trolls by singlehandedly sustaining Phil and preventing him from ever having a catastrophic day stream. This also costs him a fair chunk of change, and nobody has ever appeared as OMM or the other names to take credit, and Phil once blew up on another whale for using the name SilentBob, despite it being a pop culture reference, suggesting that this whale is in a class of their own who is getting some kind of communication from Phil outside of public view. Plus, OMM was active before OiC appeared.
I don't think Phil talks to all of his whales, but he talks to whoever OMM is. Phil seemed to have actually indulged a relationship with Jeff, confirming that they spoke off-stream.
I know people like to brand OiC as the boogeyman, but this whole thing stinks of Jeff.
Assuming it's not the odor of his decaying wife under the floorboards. Heyooo.