When phospholipids are suspended in water they can form a variety of structures. In all cases the hydrophilic phosphate region interacts with water and the hydrophobic fatty acid regions are excluded from water and form hydrophobic interactions.
One structure that can result when phospholipids are suspended in water is shown below. A bilayer of phospholipids forms a sphere in which water is trapped inside. The hydrophilic phosphate regions interact with the water inside and outside of the sphere. The fatty acids of the phospholipids interact and form a hydrophobic center of the bilayer.