Explain how soap functions, making reference to its phospholipid properties.

When soap is agitated in water, structures called micelles are formed.
Soap is comprised of phospholipids, which have a polar end and a non-polar end. The polar ends, these being the phosphate heads of the phospholipid structure, are drawn to each other in a certain configuration, whereas the lipid (fat molecule) ends have a balanced non-polar structure such that they are neither drawn to nor repelled from each other.
Water, like the phosphate heads in soap molecules, consists of polar molecules that are drawn to each other. So when water (a polar substance) is agitated with lipids (which are non-polar substances) and soap particles (polar at one end and non-polar at the other), the water and phosphate heads of the soap particles are drawn together forming spherical micelle particles.
A bi-product of this action, and the key to how soap disperses fats in a water solution, is that the lipids/fats that are suspended in the agitated water solution are collected into the center of the soap micelles.
Essentially they are forced out of the way of the polar substances (the water and the phosphate heads of the soap molecules) and collect on the inside of the micelles.
They are neither drawn to nor repelled by the lipid ends of the phospholipid structure of the soap, but nevertheless end up in their vicinity (inside the micelles) because of the dominant polar environment of the solution of water they are in.  
http://jan.ucc.nau.edu/lrm22/lessons/polar_nonpolar/polar_nonpolar.html

http://sphweb.bumc.bu.edu/otlt/MPH-Modules/PH/PH709_BasicCellBiology/PH709_BasicCellBIology4.html

Soap is widely used to clean all sorts of objects and it is able to do this so well because of the polar nature of phospholipids.
A polar molecule is a molecule with a net dipole moment resulting from the asymmetrical structure of its atomic bonds. A net dipole moment means that one side of the molecule is slightly positive and one side is slightly negative. This is the unique property of a polar molecule that makes soap so useful for removing dirt and grease from our hands and makes our dishes clean.
A phospholipid, as a polar molecule, has two ends due to this net dipole moment. The head of the phospholipid is attracted to water (hydrophillic) and the tail of the phospholipid is attracted to lipids (lipophillic) and repelled by water (hydrophobic). This is a useful combination for cleaning because the phospholipid's lipophillic tail grabs on to dirt and grease while the hydrophobic head sticks to water and gets washed off.
All of this wouldn't be as effective without mechanical effort, which is why it is important to vigorously scrub when washing. This not only helps mechanically remove dirt and grease from the object but also assists the phospholipid by pushing the lipophillic tail into as many lipid surfaces as possible before the hydrophillic head gets carried away by water during rinsing.