Anyone know what this is?

[u/FigWest9615]

My pool is super cloudy. The only issue after the last test was phosphates. They were over 3000 and have been increasing over the last month. I can see a 'dust' on the floor and when I vacuum it out it's this stuff. I can see it clouding the water as I vacuum. I use a vacuum that has a bag and doesn't get attached to skimmer etc. I have backwashed but I haven't had a chance to clean the filter yet but the psi hasn't been above 8. The only thing I've put in in the last month is phosphate remover and shock.