Phospholipids are synthesized in the cytosol. Where does the cell get the phospholipids that are found on the outside of the phospholipid bilayer and how do they get there?

The endoplasmic reticulum synthesizes the phospholipids and are transported to the membranes. The smooth endoplasmic reticulum is closely associated with phospholipid synthesis.

The phospholipids of the components of the internal membrane system are transported through transport vesicles.