Dicalcium phosphate (CaHPO₄, also called calcium hydrogenorthophosphate) has its own subheading at 283525 because of its distinct stoichiometry and widespread use in animal feed and food supplements. Other calcium phosphates — such as tricalcium phosphate — fall under the residual 283526 subheading. The classification turns on the calcium-to-phosphate ratio and the specific compound identity.

Food-grade phosphates intended for direct food use or food-contact applications are subject to FDA oversight. Importers generally need to ensure the product meets applicable food-additive specifications (such as FCC grade standards), that the foreign manufacturer is registered with FDA, and that the shipment is accompanied by a certificate of analysis confirming purity and identity.