No, I completely understand. But the fact that my starfish is dying doesn’t require immediate action?!
In general, starfish are a pain in the butt, and often die for a variety of reasons.
I'm not aware of any reason why a starfish would die specifically because of high phosphates, granted this could happen, but I'm not aware of anything.
You do what you want to do mate.
If you want to water change, knock yourself out, water changes are generally a good thing.
My point regarding your phosphate issue specifically, is that I would bet money on it your PO4 is NOT 2ppm. You would need to be pouring food into your tank to achieve that, and as you said, you've not had any fish for 90 days and have been doing weekly water changes, so it's doesn't add it.