If you have it, go ahead and use it. Do not let it tumble, it will pulverize.
I prefer Seachem's Phosguard - it's the same stuff but it's spherical. More surface area for better contact with the water.
It will help take care of phosphate problems, but the other part of the equation is solving the problem of how phosphates are getting into the aquarium in amounts that regular water changes aren't taking care of.
Jenn