My first comment is to check your test result, .9 is the highest but may also mean test error. Watch several youtue videos to make sure you do the test properly, you have to follow the instructions super precisely or get error reading.
If your phosphate really is that high, then I would guess you have phosphate leaching from your rocks. How old is your tank? Did you start with dry rocks?
It kind of seems to me like your canister filter is causing your nitrate problems, it is the so-called "nitrate factory". You should be cleaning that thing out very often, every few days, or it collects and builds up nitrate. Consider removing it alltogether, see how your tank runs without it. In my opinion, canister is very unneccassary.