I receive about 20 spam calls per day. In contrast, I receive about 0.2 legitimate calls per day. Google itself suspects that these are spam calls, because it pops up a bright red "SUSPECTED SPAM CALLER" warning when the phone begins ringing. And yet, I have found no option to have the phone automatically decline the call. There's not even an option to silence the ringer for any call not from my contacts; I actually…
Strangely enough, given Android's comparatively-customizable nature, I think this is an area where iOS does it better? (Others might correct me.) iOS 10 added "call blocking" as an app-type, which lets you choose apps which can filter phone calls for you. They can flag calls as possible-spam, or completely block them. (See [1] for Hiya's options screen, as an example.) An "only ring for my friends" feature is sort of…
You have also been able to limit ringing while in Do Not Disturb to starred contacts only, or even just "contacts" to eliminate the need to manage it like you mentioned [2].
[1] https://play.google.com/store/apps/details?id=com.webascende...