Phone numbers are being spoofed so while you might block the majority of those calls you won't be able to block all of them. The problem has to be solved upstream.

Is that just blocking calls with unknown caller ID or calls that are not in your contacts list?

In my phone with LineageOS, the option was to block anyone who was not in the contacts list.

That's a blacklist, "Don't accept calls from X". A white list would be "only accept calls from Y". That's what GP seems to be asking for.

Block unknown callers is a whitelist though. It's literally "block everyone not in my contact list".

You might want to verify that. Last time I checked, android's block unknown caller option just blocked calls where caller ID was blocked (aka "private").

...until and unless the phone number is spoofed. Then the blacklist is getting onto the whitelist.

Technically you're right, but what are the chances that a bad actor is going to spoof one of the phone numbers in your contact list.

I mean, the odds of them hitting that are so close to zero I don't even want to think about it.

Years ago, spam emails were sent to random email addresses found on the internet.

Now spam emails are sent to live email addresses harvested from peoples' activities

Today caller ID is spoofed not even with random phone numbers but specifically phone numbers with area codes relevant to you. For me, it's phone numbers of my area code which I have zero contacts in. Or it's phone numbers from my phone's registered address in Houston.

What makes you think it won't be long before fraudsters are able to connect the phone number they're calling with people likely in your contact list by ... looking up leaked contact lists?

It depends on the phone, but I'm pretty sure there are still devices where "Unknown number" /= "Number not in my contact list".