I’ve used AT&T Call Protect for years, and it blocks at the network level, which is the amazing part. So despite rampant scam calling, I get relatively few. I also have Hiya installed and active. (Hiya’s list is used by AT&T, but the mechanism in iOS works a little differently.)
So first, a lot of calls never get to me; second, sometimes my phone lights up and then stops ringing, as AT&T apparently caught it mid call; third, calls that get through are marked about 95% of the time as “spam” or “suspected spam” or “telemarketer.”
What’s great is that I’m not sure it’s 95% because I don’t think I’ve gotten 20 calls in the last two months—probably more like 10 to 15—that I’ve had to even deal with, where 1 has gotten through.