The phosphorous cycle is the simplest of all nutrient cycles operating in any ecosystem. This heavy molecule never goes to the atmosphere; it is always part of an organism, dissolved in water or in the form of rock. When rock with phosphate is exposed to water (especially water with a little acid in it), it rock gets weathered and goes into solution.
Phosphorous is major constituent of DNA, RNA and of course ATP (adenosine triphosphate). All organisms need phosphorous. Autotrophs, (plants) take up phosphorous in the form of phosphate, as roots of the plants absorb it form soil. Heterotrophs (animals) obtain their phosphorous from the plants as they eat food. Animals need large quantities of phosphorous to make bones, teeth and shells. When animals or plants die (or when animal defecate), the phosphate may be returned to the soil or water by the decomposers. There, it can be taken up by another plant and used again.
The mining of phosphate and its use as fertilizer greatly accelerates the phosphorous cycle. The phosphorous carried by water causes local overabundance of phosphorous, particularly in coastal regions, at the mouths of rivers and any place where there is a lot of sewage released into the water. Local abundance of phosphate can cause overgrowth of algae in the water; the algae can use up all the oxygen in the water and kill other aquatic life. This is called eutrophication.
Marine birds play a unique role in the phosphorous cycle. These birds eat marine fish, which is rich in phosphorous. Their excreta celled 'guano deposits' contain high level of phosphorous and thus marine birds return phosphorous from the ocean to the land.