Sounds like you might have bad hardware or a corrupt install. Phone app freezes should be exceedingly rare, to the point of nonexistence for most users. I assume you have not jailbroken your phone?
I frequently hit bugs in the Phone app in iOS too (eg can’t answer incoming call). When I used Android it was even worse. I just assumed that was a common experience but nobody cares.
Yea, I have a 7+ with no issues. Also a 6 that still works fine after the latest updates.