SOLVED!
my iphone 7 plus phone app freezes randomly, also. tried all mencioned procedures, with no results at all.
till i noticed some strange contact entries, with no data inside at all, and named "no name" or something like that. they were assigned to #.
so i followed these steps:
-delete any app in relation with contacts (cleaners, duplicate finders, etc) except stock app, of course.
-turn iphone off, and on again
-in settings, email, go to every email account, one by one, and set contact control box to off. except icloud account if you got it.
now try to use phone app normally. if it works ok, check out your contacts. if its ok, activate contacs on just ONE email acount. try to use it again, if its ok, check out contacts again. if no streange entries, activate the second one and so on. this is just to isolate which account causes the bug, which was the the origin of my app to freeze continously. i can say it was a microsoft exchange type, a hotmail account in my case. so try to repair it or delete the account.
hope it helps
greetings from spain.