Open the Phone app
Tap Settings
Tap Blocked numbers or Call settings
Turn on Silence unknown callers
On iPhone, go to Settings
Tap Phone
Turn on Silence Unknown Callers
On Android, open the Phone app
Tap the three-dot menu
Tap Settings
Tap Caller ID and spam or Blocked numbers
Turn on unknown caller blocking or call screening
Use Do Not Disturb to allow only contacts if needed
Add important numbers to your contacts
Check carrier spam-blocking options in your account or app