Why do phospholipids form a bilayer in water?

Phospholipids have hydrophobic (water fearing) tails which face each other to form the core of the bilayer while their polar (hydrophilic) head groups face outward.

Explanation: Phospholipids are components of cell membrane. Phospholipids are made up of two parts: the polar (hydrophilic) head group and the nonpolar (hydrophobic) tail. The non polar tails of the Phospholipids are water fearing while the polar head groups are water loving, therefore when phospholipids are mixed with water the hydrophobic tails arrange themselves in a way that they will not come in contact with water molecules. The hydrophobic regions of the lipids face each other forming the interior of the bilayer while the polar head groups face outwards interacting with the surrounding water.