If it's stuck on the lock screen, i.e. frozen, try a simulated battery pull, aka hard reset by holding your Volume Down and Power buttons simultaneously, might take between 5 and 20 seconds to initiate the reboot. Screen will go dark, then the phone should power back up on the splash screen. You may have to use the Power button to wake it up, and see if that gets you to where you can use your unlock screen again.