Manage blocked list/blocked contacts on the Phone app
Go to Settings-> Phone-> Call Blocking & Identification to see or manage the contacts and phone numbers you've blacklisted. From the Settings menu, you can also add new Block Contacts and Edit or Unblock numbers.
unblock calls/contacts on your iPhone 8 Plus
Follow these procedures if you change your mind and want to unblock contact from your blocked list:
From the Home screen, choose Settings.
To use the app, tap Phone.
Select Call Blocking & Identification from the drop-down menu.