I never answer calls that are not in my contacts.
It seems the phone app should have the ability to silence any call not in contacts and send them straight to voicemail. I do this manually every time I get a call that is not from my contacts. Seems like a very simple feature that a lot of people would want.
In the Republic Wireless App, there is “Call and Voicemail Settings”. In there is “Configure spam call blocking”. I suggest that as the perfect place to add an option to “Silence calls not in Contacts”.