In order to get this fieldsfield's value - you will need to query the Contact after inserting it. Since this field is a concatenated field -, it is null in the instance that you are requesting it. All you will get from your save result is the new Id value.
This behavior is the same as any other formula field in Salesforce. The value is created upon insert for this. Salesforce will only return you the fields that you have in your Contact instance and ONLY additionally the Id of the object upon insert.