Try each of the following steps in order until the error is resolved:
  1. Include the phone number address import ID in the data file to specify to which address the phone number should link. Make it the same as the address import ID (AddrImpID)
  2. Adjust the address import ID (AddrImpID) to less than 20 characters
  3. Change the field extensions on the Fields tab so that they are the same

NOTE: If you are validating the import file and the address is new, you will also receive this error. This is because the validation looks for the address import ID in the database, but the address isn't in the database yet. When importing, it first imports the address so when it looks for the address import ID, it does exist and should import properly.

Refer to How to import new phone numbers and update existing ones (BB2023) for complete instructions on importing phone numbers