To find the "Silence Unknown Callers" feature on an iPhone, follow these steps:

1. Open the Settings app on your iPhone.
2. Scroll down and tap Apps.
3. Tap Phone.
4. Scroll down to the Calls section.
5. Tap Silence Unknown Callers.
6. Toggle the switch to turn it on.

When enabled, calls from numbers not in your contacts, recent outgoing calls, or Siri Suggestions will be silenced, sent to voicemail, and appear in your recent calls list. Calls from known contacts and recent callers will still ring normally

. This feature helps reduce spam and unwanted calls by automatically silencing unknown numbers without notifying you while the call rings. However, important calls from unknown numbers may also be silenced if they are not saved or recognized by Siri Suggestions