1. Using the Phone app:
Open the Settings app on your iPhone.
Scroll down and tap Phone.
Scroll down again and tap Blocked Contacts.
Here, you will see a list of all the phone numbers you have blocked from calling or messaging you. You can also unblock any number from this list by swiping left on the number and tapping Unblock.
2. Using the Messages or FaceTime app:
Open the Settings app on your iPhone.
Tap Messages or FaceTime, depending on which app you want to check blocked numbers for.
Under SMS/MMS (for Messages) or Calls (for FaceTime), tap Blocked Contacts.
You will see the same list of blocked numbers as you saw in the Phone app. You can also unblock numbers here by swiping left on the number and tapping Unblock.