Hello 
I've completed all the tasks on the Formula Fields page. After completing the challenge I get this message:

There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: REQUIRED_FIELD_MISSING, Required fields are missing: [Phone_Number__c]: [Phone_Number__c]

Can anyone help?

Thanks in advance - Tami