Q: Screen locks pre-set msg when receiving a call

Hello mia2005,

Thank you for using Apple Support Communities. It's my understanding that your iPhone intermittently becomes unresponsive when receiving calls. I know how important it is to be able to answer calls without issue. I am happy to help get this resolved with you.

 Please try the following steps:​

1. If you have a case or screen protector on your device, try removing it.
2. Clean the screen with a soft, slightly damp, lint-free cloth.
3. Unplug your device.
4. Restart your device. If you can't restart it, you can force restart your device.

If the screen on your iPhone, iPad, or iPod touch doesn't respond to touch

Since you stated the issue occurs specifically when receiving a call, it's possible the software or content is causing this issue. If you try the steps above and the issue persists the next option would be to restore your iPhone using iTunes on a Mac or PC. Restoring takes the phone back to factory settings so it's extremely important you back up first. The following links provide information on back up options as well how to restore:

How to back up your iPhone, iPad, and iPod touch 

Use iTunes on your Mac or PC to restore your iPhone, iPad, or iPod to factory settings

Have an amazing day!