In order to block anonymous / private callers, you need to add a simple rule to your phone system's Global Blacklist. Instructions below:
- Log into the PBX Admin portal
- Go to Call Control > Blacklist
- Click "Blacklist a Number"
- Set Telephone # to 0000000000 (exactly 10 zeros)
- Set Notes to "Block anonymous calls"
From now on, anyone who attempts to call in anonymously will be treated with a busy signal.