Fwiw, Android actually does do this. When the phone is unlocked, calls show up as a banner. In addition, they added that new call screening option, I've been using it and so far it has worked fairly well. Also, there is some built-in call filtering and third party apps as well, though I have mostly been able to rely on the built-in filtering.

Does iOS really not have any options for filtering? I swear last time I had an iPhone (running iOS9) there was Something... but then again, I was jailbroken.

It's a bit funny that we got full web browsers on phones before proper call filtering.

(Disclaimer: I work for Google but not on phones.)