Open the Settings app
Tap Phone
Tap Blocked Contacts
Tap Edit
Tap the red minus icon next to the number
Tap Unblock
Or swipe left on the number and tap Unblock
To unblock from Messages, open Settings
Tap Messages
Tap Blocked Contacts
Tap Edit
Tap the red minus icon next to the number
Tap Unblock
To unblock from FaceTime, open Settings
Tap FaceTime
Tap Blocked Contacts
Tap Edit
Tap the red minus icon next to the number
Tap Unblock