Hobbyists are asking a lot out of a small handheld, hobbyist grade tester. Phosphates are tough enough to test accurately with multi thousand dollar benchtop lab grade instruments much less a handheld and expect accuracy or repeatibilty in the ppb or ug/L range. I wish I still had it but back in my private water utility management days I had a colleague who did a talk at an AWWA convention using common measurements for real world comparisons. Things like a drop in a Boeing 747 fuel tank, or grains of sand in an olympic size swimming pool or such and it really made people realize what these levels mean. This was back when the EPA was first talking about Arsenic in drinking water and the 5 parts per billion MCL which was and still is ridiculous but that is a different story.