I have a similar issue with an iPhone 7 plus screen I just tried replacing. After installing the replacement screen. The phone would restart when trying to make a call. So I put the old screen back on, then the ear piece speaker would not work, everything else would. Tried reseating the camera/earpiece cable and now the cracked screen does the same as the replacement screen, it restarts when I try to make a phone call. I see posts stating that it could be the cam/speaker cable, so that is what I have on order, for now, the customer is without a functioning phone.