Can I block calls based on a specific number prefix or pattern? Is it possible to block calls starting with a specific number? For instance, I want to block calls from numbers starting with 1408 as they are all spam calls. The digits following these four, keep changing.
If you're looking for a free and ad-free/in-app-purchase-free app, you can use the open-source NoPhoneSpam, which is available on F-Droid (though not Google Play). It supports blocking calls from individual numbers and from numbers that match a pattern with wildcards.

This is especially useful for blocking "prefix spoofing" calls, that appear to start with the area code and exchange (next 3 digits) of your phone number, but really are from random law-breaking telemarketer bots.