Spoofing is not the same thing as blocking a phone number.  FCC rules require telephone companies to make phone number blocking available and free for all calls between states (each state makes its own rules about calls that stay within the state).  If you receive a phone call from an “unknown number,” that phone number has been blocked but not necessarily spoofed. Also, you can legally block the transmission of your phone number when you make calls, so your number will appear as “unknown.”