All foods contain substantial phosphate, but unless they have added phosphate (like some fresh, canned and frozen seafoods for people do), I am not certain that any particular type of food has more phosphate relative to other nutrients like protein than do other types. One thing that adds a ton of phosphate is anything that has bones in it, including whole fish.
Ron Shimek analyzes some foods here:
http://web.archive.org/web/20010720071031/http://www.animalnetwork.com/fish/data/foods.asp
I've calculated the phosphorus to protein ratio for these foods, and I get:
Formula Two...........................176
Formula One.............................69
Frozen Brine Shrimp................232
Frozen Plankton/Krill...............182
Golden Pearls..........................273
Lancefish.................................244
Nori..........................................221
Plankton Gold Flakes...............169
Prime Reef.................................69
Saltwater Staple......................500
Silversides...............................952
Tahitian Blend..........................318