Phosphate is a polyatomic ion, meaning it's a group of atoms bonded together with a charge. It's represented as PO₄⁻³

The question you're asking doesn't have a single answer.

* The atomic number of phosphorus (P) is 15. This is the number of protons in a phosphorus atom.

* The atomic numbers of oxygen (O) are 8. There are four oxygen atoms in the phosphate ion.

Therefore, you can't get a single atomic number for "phosphate" because it's a combination of different elements.