The phosphorous sinks are the ocean and ocean sediments.  

The ocean holds $3 \times 10^{15}$ moles of phosphorous.  

The annual amount of phosphorous input into the ocean, as well as the amount of burial of phosphorous as sediment is on the order of $10^{10}$ moles. 

The sediment is of three categories:

1. Phosphorous associated with calcium carbonate
2. Organic phosphorous (associated with organic carbon)
3. [Apatite][1]

See [Phosphorous Accumulation in Marine Sediments and the Oceanic Phosphorous Cycle][2] for a detailed analysis.


  [1]: http://en.wikipedia.org/wiki/Apatite
  [2]: http://web.mit.edu/qhorn/Public/Reef%20Aquariums/Phosphorus%20articles/Delaney%20Global%20Bio%20Cyc%2012%204%201998.pdf