Principle of similarity compatibility 。 Easily soluble in water belongs to water phase, while insoluble in water belongs to oil phase, also known as organic phase. A little more simple: the substance is mixed with water, and the result is that it can become a transparent solution in the aqueous phase; Stratified or turbid belongs to oil phase.
For example: water phase - water, glycerin, alcohol, acetone, etc; Oil phase—— Liquid paraffin , silicone oil, vaseline, etc 
