How can you hard reset your phone if the screen is frozen and holding the home and power button doesn’t work?
If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support
It is really called a soft reset and it is achieved by holding down the Volume Down and the Power button at the same time until the device turns off. You can release the buttons when you see the white screen with the Apple logo.
A hard reset is the same as a factory reset where all data is wiped from the phone and it it reset to the same state it was in when you took it out of the box and powered it on for the first time.
