I would say yes but I cant prove this. Biological processes ,eg the fish making and breaking down bone makes phosphate in thier waste. If as is often the case with complete food it is high in protein bulking agents,put simply it has much much more nourishment in it than fresh frozen,there fore you have to feed much much less.
I dont ever have a problem with phosphate ,but ive recently put some good grade charcoal in the sump,so I expect to see some. In anticipation I have also put some phosguard in there.
Rest assured that the test kits we use will not detect the very lower levels of both phosphate and nitrate,so when I say my results are zero ,they in fact are not,just undectable.
All I could suggest is that may e you overfeed? My fish only get one cube if say mysis twice a week ,simetimes ince a week ,thier fat and happy on that.