am not able to delete an incoming phone number after completing the call

Hey, pengwin60.

I see that you're unable to delete a phone call on the Recents list of the Phone application. I'm happy to help.

View and delete the call history on your iPhone -- This article provides the information and steps that you need.

Restart your iPhone, iPad, or iPod touch -- If the record of a call just simply won't delete, restart your iPhone. Once it's returned to the Home screen, try to delete an individual record.

How to back up your iPhone, iPad, and iPod touch -- If restarting your iPhone didn't resolve the issue, please be sure to have a fresh backup to keep your personal information safe. In order to back up your Health data, the backup needs to be encrypted. iCloud does this automatically, but iTunes doesn't. If you'd like to use iTunes to back up your iPhone, refer to this article: About encrypted backups in iTunes

If you can't update or restore your iPhone, iPad, or iPod touch -- When an application isn't working as expected, a good step is deleting and reinstalling the app. Since you can't delete the Phone application on your iPhone, I'd like for you to reinstall the iOS. The section titled "Put your device in recovery mode and set it up again" will walk you through all the steps to reinstall the iOS software on your device. See if you're able to delete an individual record again.

Let me know how that goes, and take care!