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Have a weird one have an iPhone 6s works great but when a call comes in screen stops working can’t answer and phone will continue to ring until I do a hard reset. I have taken it apart and cleaned it no water damage have replaced the screen install a new battery.
Fix for iPhone keeps ringing but screen freezes: I know this is an old thread, but maybe it will help someone else. This happened on my Mom‘s iPhone 6. It started after I enabled Announce Calls for “Always” for her (under Settings/Phone). I turned off Announce Calls and the problem was fixed. The feature works on my iPhone 8 so it also could be a software update issue.
I would check and make sure there is not a software update that is missing. Sounds like a software issue. Go to setting ->General->Software Update and See if it shows and update that is needed. Best of luck.
