Well, you don't actually know that. A TDS level of 187 just means there are things dissolved in the water, it doesn't tell you if any of it is phosphate. You'd have to test the water for phosphate to be sure. I agree that getting the phosphate down is a priority. Water changes, good feeding habits, macroalgae in the sump, and chemical media like GFO are probably the safest way for beginners to go about reducing a high phosphate level in an up-and-running tank.
What is also a bit concerning though is your alk is a little on the low side if you are keeping any calcifying organisms, even coralline would probably like it higher. 7.5 dKH is really as low as you want to see it, but because of the intrinsic error in our test kits IMO it's better to keep the level constant and >8 dkh. It would probably be good for you to dose your tank up to about 8.0 with bicarbonate (regular old baking soda from the grocery store), and then watch how much it consumes over about 48 hours to see if you need to start dosing. If you do, kalkwasser will probably handle all your Ca/Alk needs and give your pH a bump if you are still worried about it.