Try a restore via iTunes.
If that does not work, do and Update.
After that, if you still have concerns, contact Apple Support.
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
Try a restore via iTunes.
If that does not work, do and Update.
After that, if you still have concerns, contact Apple Support.
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
How much storage do you have available cause from what I've seen and sometimes helps is to have a minimum of 2GB of space of storage open for the phone to breathe..
iphone constantly freezing