You could try two-color fluorescent detection. Use one color for your protein, and a general p-Ser, p-Thr, or p-Tyr antibody in the other color.

Phosphorylation may cause a mobility shift you can pick up on a Western, especially if there is more than one phosphosite. You could treat your samples with phosphatase to see if the mobility changes. Not sure if this would be precise enough, but it's a place to start.

Thanks alot Amy, I just know it is having precisely PKC and PKA phosphorylation sites