Open the Phone, Messages, FaceTime, or Contacts app
Tap the contact or number you want to block
Tap the info button or contact details
Scroll down and tap Block this Caller
Tap Block Contact to confirm
To block from Settings, open Settings
Tap Phone, Messages, or FaceTime
Tap Blocked Contacts
Tap Add New
Select the contact to block
To block unknown callers, open Settings
Tap Phone
Tap Silence Unknown Callers
Turn it on