Achieve question 3

[IMOGENE GAEDE 1E]

Hello, I was confused about resonance structures in problem 3 of the Achieve assignment. The instructions said to draw the resonance structure that "minimizes formal charge" and I had trouble with drawing a phosphite ion. Can someone explain to me why my original Lewis structure (the top drawing) is incorrect (the second one is my attempt that was correct). They both have a total formal charge of -3 (the charge on the ion), but why is it 'better' to have charges on the oxygens as opposed to the phosphorus? Thanks!

[Christa 2I]

Since oxygen is a more electronegative element than phosphorus, it makes more sense that oxygen would have a greater pull on the shared electrons, resulting in negative formal charges on the O atoms rather than the P. Additionally, your second drawing gives phosphorus an octet.