my iphone 8 was dropped and the screen is black. the phone is still on I can hear it ring , but no picture / anything on the screen. I scared that if I turn it off a cant see the screen to input my pin number to reopen the phone. what can I do?.

Unless you had Never as the timeout interval the phone is locked already.

You will have to have it repaired and when you get it back you will probably have to wipe it and restore your last backup

First try a Forced restart Force restart iPhone – Apple Support (UK)

If no better you should arrange a repair iPhone Repair - Official Apple Support

Or

 Contact - Official Apple Support

Anything other than Screen or Battery may be a replacement phone and the price is in the article under "Other damage"

When it comes back see also

iPhone unavailable, Passcode forgotten, iphone Locked, or Disabled

You can sometimes remedy this without a computer if on iOS 15.2 or later by tapping on "erase iPhone" , but you will still need the Apple ID password. It will WIPE the phone, no choice!

How to reset your iPhone, iPad, or iPod touch when you forgot your passcode - Apple Support

video

https://youtu.be/7s8-zLG9ySQ

 ios 15.1 and earlier:

If you've forgotten your iPhone passcode – Apple Support (UK)

Your mobile phone may fall too far away, causing the screen not to appear. You don't have to worry about not being able to enter your password or ID. This is because you should take the mobile phone to the repair shop for repair and replace the mobile phone screen for normal use.

- Chinese users

Thete is no guarantee that, after replacement, you can use the same passcode successfully.