A bit of history...we NEVER treated pools for phosphates for many years until someone discovered that they could sell very inexpensive Lanthanum salts to remove phosphates from pool water and that pool stores could make a lot of money doing so. All of a sudden phosphates were the scourge of every pool and if we did not get rid of them our pools would turn green and stay that way. Funny how all we needed before these products was chlorine! Anyway, China has greatly increased the price of the raw material (Lanthanum salts) so the profitability if going down and I expect that we will see a lot less emphasis on phosphate removers.
Also, nitrate is an algae food also but since the only way to remove nitrate is by water replacement the chemical companies and retailers cannot sell us anything to remove the nitrate at a profit so they just don't talk about it nor do we test for it.