Yes, it will likely need to be replaced more often in the beginning. You should test your mix water and see if this is the source (versus your rocks leaching, etc.). If so you may want to mention this to your LFS so they can change their filters. Lots of sources of phosphates out there so it may not be your water.
Called the LFS and they think the phosphates came from me washing the sand in tap water before putting it in the tank and that w/cs will fix it.