Force shutoff iPhone 8 Plus

I dropped my iPhone 8 plus, and now the display is broken. It is completely unresponsive to touch, and the screen just shows some rainbow lines, distorted text. A good amount of the display is dead, just black. Everything else works: the haptic system and speaker still works. The phone has alarms that still go off, and to shut them off I press the power button, but that just snoozes them. They go off again after 10 minutes or so. How do I kill this thing? Siri doesn't seem to work so I have to manually kill this thing. How can I do a force shut off?