The answer is; hydrophilic heads; hydrophobic tails
The hydrophilic heads of a phospholipid are composed of a phosphate and glycerol molecule. Since the phosphate has a charge, the head are able to interact with water molecules through hydrogen bonds (Remember water is a polar molecule). The hydrophobic tails are composed of hydrocarbon chains that are uncharged hence do not interact with water. When phospholipids are immersed in water, they form a bilipid layer - with the hydrophobic tails clumped up together in the center and the hydrophilic heads on the outside.