I don't know anything about Philip's path to get where he is now, but there are a number of videos of Philip using his current method of communication, which appears to be typing on a bluetooth keyboard to an ipad app that repeats his letters and words back to him.
The mom holds the keyboard, but Philip moves his own hand. Mom seems to use a lot of cues to help him keep on track--shaking the keyboard to bring him back to it, repeating his words back to him--but I really don't see her writing it for him, moving the keyboard under his finger to spell things, or "interpreting" vague gestures.
https://www.youtube.com/watch?v=MK_Q60LhgzA
This one has several minutes of typing where you can see the keyboard and his hand. It's slow, slow going, but it really looks like he's the one doing the writing.