changed Phone.PartyId to Phone.Party (nav property) for the EF entities and removed the PhoneModel.PartyId property completely. all tests pass. This change affected the results int of the PartyContext.SaveChanges() method, proving that this value is based on 'objects affected' rather than 'rows affected', since the value increased by the number of added nav properties in the saved object graph and also does not increase when an entity is split across multiple tables.
fixed EF configs to name the Phone.PartyId FK column the same as it was previously, and not Party_PartyId.