In order to block spam or unwanted calls on your Cisco IP Phone Series 8811 or 8851 please do the following
1. Select the Gear icon on your phone and go to Recents
2. Navigate to the phone number you would like to block and press the 3 dots until you see the option Mark Spam
3. On the next screen select either Potential fraud if you want the call to be rejected or Telemarketer if you want to allow the call but flag it as a Telemarketer
4. To remove a number from your Spam List press the Gear button on your phone, go to settings, scroll down to Spam call list, select the number you want to remove and hit Unmark Spam
Note: The phone only supports 150 numbers to be added to the list.