Open the Phone app
Tap Recents
Find the spam number
Tap the info icon next to the number
Scroll down and tap Block this Caller
Tap Block Contact to confirm
Go to Settings
Tap Phone
Turn on Silence Unknown Callers
Go to Settings
Tap Messages
Turn on Filter Unknown Senders
Use a call-blocking app from the App Store
Contact your carrier to enable spam call protection
Report spam numbers to your carrier
Delete and avoid answering suspicious calls
Add important contacts to your Favorites list