Open the Phone app
Tap Recents
Find the number you want to block
Tap the info icon next to the number
Scroll down
Tap Block this Caller
Tap Block Contact to confirm
Open Settings
Tap Phone
Tap Blocked Contacts
Tap Add New
Select the contact to block
Open Messages
Open the conversation
Tap the contact name or number
Tap Info
Tap Block this Caller
Tap Block Contact to confirm
Open FaceTime
Tap the info icon next to the number
Tap Block this Caller
Tap Block Contact to confirm