Old screen( no grounding clips/tabs) doesn't match replacement screen

We've been seeing this a lot on the newer model iPhones like yours. What's happened is that when removing the screen you've managed to separate the screen's mounting frame from the screen itself rather than from the phone frame like it's supposed to. My personal suspicion is that Apple has changed the kind of adhesive used to mount the screen frame to the display assembly, and the new stuff just doesn't hold as well as the older glue did.

Anyway, compare your phone to this picture of what it should look like with the screen removed.

I'm betting you'll see the screen frame still on the phone rather than stuck to the screen like it should be. This picture of the screen is what it should look like; I'm betting yours is missing the black and silver mounting bezel; that's the part that's still stuck to the phone.

The fix here is fairly straight-forward; you just have to go around the edge of the bezel and separate it from the phone. Once it's off you can transfer the front sensor parts to the new display and continue on with the repair.