There are many privacy problems in phone call blockers such as TrueCaller leaking your phonebook (thread Does TrueCalller App leak your phonebook?) in Android phonebook blockers. I really think the support should be native. I would like to understand why it is not at the moment.
There are many threads about the feature in non-native targets by 3rd party apps but none of those threads offer a simple, strong-security and strong-privacy approach for the problem: thread Android app to to block international calls from a particular country.
Example block function: block all UK phone numbers by Regex
- +44.* so matching UK country code and any other letter after it
OS: Android Oreo 8.0
Phone: Oneplus 3T