i can't do it for him because i have relatives from abroad that contacts him.
the silence unknown caller feature only silence unknown incoming calls.
if the fella already in the contact list, the phone will ring.
again, this is only for iPhone.
another way is to put screen time lock on his Apple Account and manage his contacts for him. but this one too kiddy liao lah.
i told him before if anybody wants to contact you from abroad, they can do so via whatsapp because we all have family/relative whatsapp groups so there is no need for him to answer unknown calls.
it is always the self-importance, self-aggrandising, chest puffing kind of "what happens if its an urgent overseas call from someone I happen to know"? (yah, what was his previous profession? diplomat? LTC and higher military attache officer?)
it's his attitude u need to change. technology blockers will not help in the long run but provide temporary relief.