The oxidation state of phosphorus in phosphate (PO₄³⁻) is +5. Here's how we determine that:

* Oxygen's oxidation state: Oxygen almost always has an oxidation state of -2.

* Overall charge: The phosphate ion has a charge of -3.

* Calculation: Let x be the oxidation state of phosphorus. We can set up the equation:

x + 4(-2) = -3

x - 8 = -3

x = +5

Therefore, the oxidation state of phosphorus in phosphate is +5.