Open the Settings app
Tap Phone
Tap Blocked Contacts
Find the phone number you want to unblock
Swipe left on the number
Tap Unblock
Alternatively, tap Edit
Tap the red minus icon next to the number
Tap Unblock
If the number is in Messages, open Messages
Open the conversation with the blocked number
Tap the contact name or number at the top
Tap Info
Tap Unblock this Caller
If the number is in FaceTime, open Settings
Tap FaceTime
Tap Blocked Contacts
Swipe left on the number
Tap Unblock