I suppose you mean like in this clip, where the green area moves with the phone.
This means that instead of this:
You want to do this:
Let’s suppose the clip with your subject (in my case the dog) is on track V1 and the clip with the green area is on track V2.
You need to add a Size, Position & Rotate filter on the clip with your subject and use keyframes to make the clip follow the green area.
Here’s a quick demo:
Depending on you own clips, you’ll probably need to use more keyframes to make your subject follow the green screen accurately.