Green screen tablet reflection AE

You can pull a pretty good key from Keylight. Unfortunately, the reflections wrap around the actor's finger. My approach would be to duplicate the footage, apply Keylight to the top copy and create a good clean matte.

Next step, add Set Matte to the bottom copy to give yourself a black and white screen that you can use as a base for the replacement screen using Set Matte, Black and White, and then maybe Exposure and Invert later.

The last step; add the replacement screen between the layers, experiment with blend modes, and tweak the settings. You can end up with something like this in a couple of minutes. 

That is probably about as good as you are going to get with this shot. I'm showing you everything that I adjusted on Keylight to clean up the key enough to make it work. No hand roto or masking was required for this shot. Because of the light wrap around the finger in the original footage, fixing that problem would require a lot more work including tracking, cloning, and color correction and I don't think the shot is worth the effort.

I almost always use this kind of layering when I am compositing replacement screens. It is important to get the luminosity right. If Keying is required I make sure that the screen color on the phone, tablet, or monitor is very dark green so that I can pick up reflections and still pull a good key. Your screen has almost the same luminance value as the skin so pulling a key is not as easy as it should be. That is a very common mistake.

Any time you shoot for color keying (greenscreen) you should keep the brightness of the screen at least 10% to 20% lower (about 1 stop) than the skin. It will really help with edge contamination. You do have to pay very close attention to the reflections and make sure that they are not too bright. Eliminating all reflections on the screen makes the composite look fake. If there are none, I'll almost always add some using blend modes. I hope this helps.

Here's the project file without footage so you can take a look. If you use your sample footage and create a new screen replacement image you should get the idea.

I would guess you need to create a matte to exclude the finger area before you add Keylight. Then you control Screen gain in Keylight.