Last night my iPhone screen froze. Phone would wake up if laid down but no buttons were responding. I put it on charger and just let it sit overnight. Tried this morning and same issue. So used iPad to research. Apparently becoming a common issue. Fix:step 1- remove case and any screen protector. Clean screen.--for me, that immediately brought it back to life. I even got case back on and it's fine and I didn't have to remove gorilla glass protector but that would have been next.
Step 2 if 1 doesn't fix it- check for software issue, do a forced restart ( which I could not do with case on). If its only one app, try deleting that app.
Step 3 reset all settings to default at general tab, which wouldn't have worked for mine since no buttons worked
Seems this is a common issue ESP with newer phones. Always glad I have iPad to look stuff up ESP whe. It's an issue with phone !
Velda