Go to Settings
Tap Phone
Turn on Silence Unknown Callers
Go to Settings
Tap Phone
Tap Call Blocking & Identification
Enable any spam-blocking apps you have installed
Open the Phone app
Tap Recents
Tap the info icon next to a spam number
Tap Block this Caller
Go to Settings
Tap Focus
Set up Do Not Disturb or a custom Focus mode
Allow calls only from your contacts or favorites
Contact your carrier and ask about spam call filtering
Update your iPhone to the latest iOS version
Report spam numbers to your carrier or voicemail provider