SCRUB your rocks with a toothbrush. Then once clean, daily keep scrubbing your rocks with a toothbrush inside your tank. Make sure you have enough flow to keep detrius off your rocks.
This is currently working for me.
Be sure to scrub your rocks in a separate container at first (your water will turn green if not) if possible then rinse with fresh saltwater (water from waterchange).
Keeping up with this maintenance will eventually lower your phosphates and prevent it from growing back. You should invest in a phosphate reactor to help eliminate the phosphates after scrubbing.