Most phosphate removals are expensive, You have media similar to activated carbon. Or polymer resin materials or Zeovit.
Another option is to grow macralgae in your sump which really works. I have been doing this for a month and the levels are gradually getting very small. UNDERFEED is the best method, but can be hard sometimes.
A decent feed every two days will help rather than twice a day.
I am sure you will get more advice on this post as everybody's posts help out in one way or another!
Good luck.
Craig