CLIR

What is a withheld number?
When a number is withheld, there is no caller ID, which means the recipient cannot see who is calling. A number can be withheld during digital, analogue or voice-over-IP (VoIP) telephone calls. The process of withholding a number is also called Calling Line Identification Restriction (CLIR). The recipient of a withheld number call usually sees a message such as “unknown” or “withheld number” in their phone display instead of a phone number.

CLIR