As Kilted Tim indicated, if it's only your favorites your phone is ringing for, you have Do Not Disturb enabled (it's a top-level setting in the Settings app, and can also be enabled and disabled by tapping the crescent-moon icon in the Control Center, which you get to by swiping from the top-right corner of the screen down and toward the center of the phone) and you have it set up to only allow calls from your favorites.
Silence Unknown Callers could be in play as well, but that would allow the phone to ring for everyone in your phone's Contacts app and not just your favorites. If any numbers that aren't ringing are in your Contacts, then the cause is definitely Do Not Disturb.
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