When outgoing call display turn black

Hello KrunalPanchal,

If the display is turning black while on a call, that indicates there could be a hardware issue with a sensor that recognizes when the phone is near and away from your ear. To help isolate the behavior, follow the troubleshooting steps in the article below, and reach out to Apple Support for additional assistance if the issue persists: 

"If your screen is too sensitive or responds intermittently to touch

1. Restart your iPhone or iPad.
2. Make sure that your screen is clean and free of any debris or water.
3. Disconnect any Lightning or USB-C accessories. If your screen works after removing an accessory, try using a different outlet, cable, or charger.
4. Remove any cases or screen protectors.

Contact Apple Support

If your screen still isn't working, you might need to set up service for your device. Contact Apple Support."

Kind regards.