How to send unknown callers directly to voicemail on iPhone (while allowing text and know callers through)

I get about 20 robocalls a day, and I'm trying to figure out how to prevent unknown numbers from ringing my phone. Some ideas: - Have a silent ring and assign that to all non-contact callers. There is currently no way to mass assign a ring (to my knowledge), so this would be very labor intensive. - Use a Google voice number and let it do all the redirects. - Use Do Not Disturb but let text and notifications through from apps I want to use. Has anyone found a good way to do dodge robocalls?