What are he two processes that must occur to phosphates before they can cycle directly from organisms to the exchange pool and back to organisms?
Since this is not my area of expertise, I searched Google under the key words "phosphate cycle organisms" to get these possible sources:
http://en.wikipedia.org/wiki/Phosphorus_cycle
http://www.biolbull.org/cgi/reprint/72/2/190.pdf
http://www.enviroliteracy.org/article.php/480.html
http://www.bookrags.com/research/phosphorus-cycle-woc/
http://www.scionline.org/index.php/Phosphorus_Cycle
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.