unknown number

noun2

1. •
   A phone number that is unfamiliar to the recipient.

   • Kelly looked at her phone. This unknown number keep coming up. Answer it. — 2012
2. •
   A phone number that is hidden from the recipient.

   • The voice on the phone sounds familiar, but the incoming call on my phone reads “ unknown.” […] And why are you calling me from an unknown number?” — 2011