From the Settings app, scroll to and tap Apps.
Scroll to and tap Phone.
Scroll to the Screen Unknown Callers section header.
From this screen, you can choose how and when your iPhone will screen calls:
To screen calls via Facetime, tap the Back icon to return to Apps settings.
Scroll to and tap FaceTime.
Scroll to and tap or slide the Silence Unknown Callers switch to ON.
This is similar to the Silence option for the Phone app, as shown in step 4.
To filter unknown numbers and spam in your text messages, tap the Back icon to return to Apps settings.
Scroll to and tap Messages.
Scroll to Unknown Senders.
Tap or slide the Screen Unknown Senders switch to ON.
Tap Allow Notifications to view more options.
You've completed the steps!
