Unknown incoming calls

I see. Then the same applies. To have the Phone app display the identity of the caller the phone number must be in the number field for the phone to recognise the person.

However, this is only possible if the incoming call itself bears the number. If it does not announce the number, your phone does not receive this information and therefore can't connect the call to a person in your contacts, and can't show you on your screen.

This is more common with fixed phones - often called landlines - which, at least where I am, rarely announce their number and are displayed as unknown caller. Businesses are more likely to allow the display of their number because they want to show a caller who is ringing but private numbers have a default setting not to show the number. Mobiles are a bit different.

The point is that if a caller has chosen not to have the number displayed there is nothing a receiving phone can do to override this.

How to resolve an unknown incoming calls on iPhone 11?

You can either answer the calls or not.

If a number is not revealed the caller does not want the number shown, just as you can choose not to show your number to those you call by going to Settings > Phone > Show My Caller ID.

Hiding a number is the caller's prerogative and not in your control. It is not a fault of the phone or a problem to be fixed.

Can you give a bit of detail about what isn't happening for you? Do you have this number in a contact card for this person - or people?

Is the phone number in the phone number field? If it is in a different field then yes, you will have it, but I don't think it will display for a call.