iPhone XR black screen an wont turn on

1. Restart your iPhone: Try this first. Simply restart your device to fix this problem. This is a very simple process. You can shut down your device by going to Settings > General > Shut Down. You can also power off your iPhone by (a) (if it is an iPhone X) pressing and holding the side and one of the volume buttons (up or down); (b) (if it is another iPhone models) pressing and holding the side button.
2. Force close the Phone app and restart: You can close the Phone app and restart again. Do not worry, this will not delete anything. Here is how:
   1. iPhone X: Unlock your device and swipe up. Now you will see the most recently used apps. Find the Phone app, and touch and hold the up and press the red minus (-) icon to close. Then tap the Phone icon and open the Phone app. 
   2. iPhone 8 and earlier models: Double press the home button. Then find the Phone app and swipe up on the Phone app card to close it.

restart Restart your iPhone, iPad, or iPod touch - Apple Support

or restore DFU mode to Restore - Apple Community