Physical Cycle Sites
Henderson's Dictionary of Biological Terms, by Eleanor Lawrence. 10th Ed.
Phosphorus is the key to energy in living organisms, for it is phosphorus that moves energy from ATP to another molecule, driving an enzymatic reaction, or cellular transport. Phosphorus is also the glue that holds DNA together, binding deoxyribose sugars together, forming the backbone of the DNA molecule. Phosphorus does the same job in RNA.
Again, the keystone of getting phosphorus into trophic systems are plants. Plants absorb phosphorous from water and soil into their tissues, tying them to organic molecules. Once taken up by plants, phosphorus is available for animals when they consume the plants.
When plants and animals die, bacteria decomposes their bodies, releasing some of the phosphorus back into the soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles from were they were released by riding through streams and rivers. So the water cycle plays a key role of moving phosphorus from ecosystem to ecosystem.
In some cases, phosphorous will travel to a lake, and settle on the bottom. There, it may turn into sedimentary rocks, limestone, to be released millions of years later. So sedimentary rocks acts like a back, conserving much of the phosphorus for future eons.