iPhone XR won't shut off
After receiving several FaceTime and Messenger video calls, my phone won't shut off. The phone screen has turned purple and the text is doubled. It won't even let me swipe up to stop that app/screen. I've uninstalled/reinstalled Messenger several times. No change. I've tried pressing the vol up and vol down buttons quickly. Doesn't work. Help. How do I reboot and hopefully get rid of this phone/messenger issue? Thanks
iPhone XR, iOS 14