Apple calls it "Do Not Disturb" - check the setup menu DND / Allow calls:
Callers with suppressed call number immediately get a busy signal or be thrown to the mailbox when activated "Do not disturb" (DND).
Families and friends who suppress their call number (call without a caller ID) can only call at certain times. For example, if you do not "disrupt" only from 18:00 to 20:00. Between 6 pm and 8 pm everyone would go through, even if the caller can not be found in the address book of your iPhone because of CLIR.
The outgoing message to your mailbox you could formulate accordingly ("landed on the mailbox only because of CLIR", ... "please next time with activated caller ID call").
If anonymous callers, stalker, automatic dialing and dialing the wrong number fax machines are to be blocked, but everyone else should call contact saved in the iPhone address book, you can find the ideal solution later in the settings menu DND / Allow calls:
This option allows the selection of contacts / groups
As soon as an automatic dialing call ("Dialer") calls at short intervals and suppresses its own number or displays a constantly changing fake phone number, "Do not disturb" must remain active, otherwise you are no longer available for serious callers!
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