My Iphone XR Nook Screen froze and when I try to turn off the phone an alarm rings. What should I do? I tried to push the volume up and release, then volume down and release then held down the power button. Nothing happened.

My phone has frozen on the nook app this morning. It will not turn off to reset. The process to reboot does not work. (Volume Up; Volume Down; off on button)When I try the traditional turn off process (Volume up and on off button) an alarm starts like a police car. I still get alerts on screen, and can read messages from alerts but cannot open the phone. The pull down quick screen will come up. What should I do?