The balanced chemical equation for the reaction between magnesium nitrate and sodium phosphate to form magnesium phosphate is:

3Mg(NO3)2(aq) + 2Na3PO4(aq) → Mg3(PO4)2(s) + 6NaNO3(aq)

In this reaction, magnesium nitrate and sodium phosphate are the reactants, and magnesium phosphate and sodium nitrate are the products. The coefficients in front of each compound indicate the relative number of moles of each substance involved in the reaction. For example, 3 moles of magnesium nitrate react with 2 moles of sodium phosphate to produce 1 mole of magnesium phosphate and 6 moles of sodium nitrate.