The compound formed between ammonium (NH₄⁺) and phosphate (PO₄³⁻) ions is ammonium phosphate, with the chemical formula (NH₄)₃PO₄.

Here's how the formula is determined:

* Ammonium ion (NH₄⁺): This has a +1 charge.

* Phosphate ion (PO₄³⁻): This has a -3 charge.

* To balance the charges: You need three ammonium ions (3 x +1 = +3) to neutralize the -3 charge of the phosphate ion.

Therefore, the formula for ammonium phosphate is (NH₄)₃PO₄.