I think of phase relationships in terms of volume-density relationships.
Jason, what are you doing up at 1am? Wait, I'm no better.
I see what you are saying but I think of vol-dens relationships more as Soil Mechanics Analysis and phase relationships more as Engineering Properties of Soils and Materials. I think of phase relationships as the three phases making up soil - solids, water, air. If I am reading the Geo NCEES syllabus correctly, it doesn't seem that these types of questions are on the exam? (Ex. questions providing/asking for water content, void ratio, porosity, degree of saturation, volume of solids/water/air, unit weight, specific gravity, etc., etc.). I could be wrong.