What is a Private Number?
A hidden number can also be known as a ‘private number’ – or any call that rings through, but does not show the number.
How To Block A Private Number On iPhone
Silence incoming unknown callers by going to “Settings > Phone > Silence Unknown Callers.” Use DND to prevent private numbers from annoying you by
adding a new DND mode and allowing calls from your contacts. Block individual callers by tapping and holding on the caller then selecting “Block Number.”
How long does block caller last on iPhone?
On an iPhone running iOS 7 or later, you can block any phone numbers you want.
Once a phone number is blocked, that phone number remains blocked on an iPhone after you delete it from your Phone, FaceTime, Messages, or Contacts apps.