Both images have to be wrapped with div and rotation transform should be applied on hover state for that div, NOT FOR IMAGE ITSELF
The back side of the flip-object should have z-index higher, than front side
I would recommend keeping front side image position: relative and only back side image made position: absolute. It will help to keep wrap div its height.
“Parent div” should have to have set Perspective, for make visual 3D effect for flip animation
Hope I was able to explain.
Cheers,
Anna
P.S. Don’t forget to find identical phone prototype images. Now there are 2 different models and it looks weird.