My VOIP vendor provides a spam-scoring system for inbound calls from an outfit called TreCNAM. Needs more participation to be highly effective, but it's an idea!

The VOIP vendor also enables call treatments that can require a caller to press a specific number after the call is connected, before it actually rings, and to whitelist specific legitimate callers. Together, those phone screening tool reduced rings from robocallers on my VOIP phone to a very rare event.