How Philip get infected (my research)

[Bad doggie. DOWN.]

Guys, this is a really simple question. He probably was purposely infected by the Tuurngait while he was unconscious from the end of Overture to the beginning of BP. That's why he was being held in that room instead of being killed, they were waiting for him to transform.

This. It's the simplest answer to the question... perhaps he was already infected prior to this point in the story (bitten by one of those dogs or spiders in the mines or by using the artifacts etc), but at this point I'd say he would definitely be infected.

This too. Of course, there's the question about whether it's canonical to say that Phillips ever really got bitten by a spider or dog, or that the Artifacts are anything more than dressed-up save points.