I didn't completely drop my phone onto Draco, but it did sort of clip him when it smacked into my hand, I was holding him at the time.
I have the IPhone 7 plus so it's a big phone, and it caught him on more of the edge of his right side. He hasn't shown any signs of being injured from it as far as I can tell. But I'm just worried
Those are big phones. If it missed his head and wasn't a direct hit I doubt it will be an issue. Look out for lethargic behavior, seizures, or swelling/bleeding which may indicate internal injury and a vet visit should be made. If he continues on as normal though there is probably nothing to worry about.