I started the task by matching the screen on the phone using the Transform node and modifying the rotate, scale, and skew parameters.
Afterward, I attached a Tracker node to the original footage and applied 4 points. In order to make the iPhone screen follow the camera movement, I selected all 4 points and created a CornerPin2D (current frame, baked). Eventually, a CornerPin2D will appear and once it is gonna be connected to Merge, the screen is gonna be tracked.
Finally, I rotoscoped each finger, adding a bit of feather in order to avoid green parts each time the fingers slide over the screen