Not sure about the best simple way of doing this, but here's how I would approach it:
1. I would edit the animation of the "phone" object and add another image point and place that point in the upper-left corner of the "phones" "screen".
2. Then I would take the other sprites, I make them initially invisible and set their origin points to 0, 0.
3. Then I would make events if sprite position(x, y) is equal to the position(x,y) of the "phones" image point, then set sprite x visible.
If it's not equal then set it back to invisible. And do that for both sprites, or if you have more sprites, create a family put them in it, and then do that event for the family.