Phosphorus and Oxygen are both non-metals; this means that this is a covalent bond, but as the difference in electronegativity(EN) is between 0.5 and 1.7, this could also be described as a polar-covalent bond depending on the grade of Chemistry you are in.
EN(P) = 2.1
EN(O) = 3.5
The difference in EN is 1.4
