How do I fix an iPhone screen that randomly turns off and freezes?

On a user-to-user online support site, no one here has the ability to run diagnostics on your phone remotely.

You will need to make an appointment at the Apple Store / Genius Bar or take the phone to an authorized Apple service shop to let them check and test the phone.

A guess...and it is just that, a guess.......the screen may be starting to fail or the power supply section may be doing the same thing.

You can find a list of authorized service shops in your area by using the link just below:

Find Locations - AppleAppleFind Locations

Good luck!

1. Follow the Apple article to resolve the issue --> If your iPhone, iPad, or iPod touch won't turn on or is frozen ...
2. If not resolved; please follow the steps in the following link for support with this issue: If your iOS device restarts or displays the Apple logo or a spinning gear unexpectedly
3. You still see a black screen after charging, force restarting, following the steps in this article.
   1. You see a black screen, but you can hear alerts, sounds, and vibrations.
   2. The screen remains black, but the device chirps when you unmute it and connect it to power.
   3. Your screen is on, but it doesn't respond when you tap, slide, or try other gestures. 
   4. You can't force your device to restart because a button is broken or stuck.
   5. Your device is stuck on the Apple logo, displays a solid color, or isn't recognized in iTunes.
   6. Contact Apple Support to set up service if you have any of the above issues:
4. Please follow the steps in the following Apple Video for support with this issue:

If none of the above steps resolve the issue, it is recommended to reach out to Apple Support or visit an authorized service center for further assistance. They can provide specific guidance based on your device model and iOS version.