I started this with simply getting a tracker attached to the original footage and then making a 4 point cornerpin track to have somewhere for the iphone screen to lock on to.
Afterwards, i took the tracking data and applied to set to input on the screen before the mirror and reformat nodes were added in, as doing it after caused a lot of distortion.
Once this was tracked properly, i went about rotoing the fingers that go over top of the screen, though unfortunately the original video has an alpha baked in and this needed to be removed.
Afterwards i went about rotoing each finger, trying to feather the sides as there’s some motion blur whenever the fingers move that was causing a lot of green to come through when not feathered.
After this i had my alphas for both the screen and the fingers merged, next was simply putting the background under it.
There are some issues with this regarding the cornerpin track not quite going exactly where i want it to and a little bit of fuzziness on the fingers, but i plan to fix this a bit with some help.