Open Settings
Tap Phone
Turn on Silence Unknown Callers
Open Settings
Tap Phone
Tap Call Blocking & Identification
Enable any call-blocking apps you have installed
Open the Phone app
Tap Recents
Tap the info icon next to the unwanted number
Tap Block this Caller
Confirm the block
Open Settings
Tap Messages
Turn on Filter Unknown Senders
Contact your carrier to enable spam call filtering
Update iPhone to the latest iOS version
Report spam calls to your carrier or the FTC