Phosphates come along with fish food. Excess phosphates WILL promote algae, however, in a well planted, established tank, excess phosphates will likely not be an issue.
As I mentioned in a previous thread I have used Purigen in the past, but can't buy the marketing hype. In my testing I found it's use did not reduce tank nitrates. For water polishing, I feel you can do just as well with inexpensive polyester fiber...I get mine at Wallymart in the craft pillow section for about $4 for a huge bag.
For 'super polish' I've been 'playing' with Marineland's somewhat new Magnum Internal Polishing Filter (approx. $45). The micron cartridge with 1/2 cup of filter grade diatomaceous earth makes for awesome filtration and glass like water!
Tip: Again, for the highest quality water, feed high quality fish food that results in less fish waste (Believe it or not!)