Using Teams Phones, it is possible to block unwanted spam calls. While there is not a proactive spam filter for phone numbers, it is possible to block calls from a specific number after it is received. This way you will not receive a call from that same number again. After spending some time blocking individual numbers, you should see a drastic reduction in the number of marketing/spam calls you receive.

1. To block a call, first navigate to the Calls screen in Teams. You will see your call history.

2. Hovering your mouse over an entry should reveal 3 dots.  Click on those 3 dots and choose Block.

3. You will now see the word Blocked next to all calls from that number.

4. If you have accidentally blocked a number that you would like unblocked, clicking on the same 3 dots will now bring up an Unblock option.