This user-friendly Colorimeters will give you direct readings in mg/L. Phosphates are present in natural waters and at concentrations typically found, do not pose any specific health threats to humans.
However, excessive contamination of water courses from agricultural fertilizer run off or wastewater/effluent discharge can promote excessive algae or plant growth.
Milwaukee offers Mi412 with range 0.00 to 2.50 mg/L.
Mi412 is supplied complete with 2 cuvets, reagents, hard carrying case, wiping tissue, 9V battery and instructions.