I recently adopted a new policy for my phone, which is similar to greylisting on mail servers.

For all unknown numbers, I try to answer the call muted. I try to avoid hinting autodailers that my number is valid by sending them to voicemail.

If I hear an autodailer, I stay muted, report the FTC violation, and add the number to my blacklist at the carrier level.

If I hear silence, I stay muted, and assume an autodailer is waiting for a greeting then add the number to the blacklist.

If I hear a human, I stay muted unless they address me. If they hang up and redial, I address them then.