Ok! So I tracked the motion using the two top corners of the screen, then stabilized the result, and that actually worked really well. The phone keeps the same width even when tilted to the side. There is a short period when the user’s thumb crosses over one of the tracking points, but I found if I deleted those specific points that were incorrect, After Effects filled in the blanks really well. The only issue I’m having now is that, when the phone gets tilted down, the screen gets longer, so not sure if I can track multiple points, for example, tracking the two top corners of the screen and then the bottom parts of the screen in relation to the top portion.
The only other issue is there is some noticeable jitter left in the video, but I should theoretically be able to export as an AVI, then re-import and use the 3D tracking stabilization.
Fortunately, the user’s left hand holding the phone stays pretty stable, so it’s just the right hand that tends to cross over the bottom on the screen making it more difficult to track that lower screen portion