Answer
Final compound formed has the formula $K_{2}HPO_{4}$.
Work Step by Step
The metal cation is $K^{+}$
The polyatomic anion is $HPO_{4}^{2-}$
Combine 2 $K^{+}$ and 1 $HPO_{4}^{2-}$ to balance the charge.
Final compound formed has the formula $K_{2}HPO_{4}$.