As we can clearly see in the structure,

the number of $\mathrm{P}-\mathrm{OH}$ bonds is 4.

The oxygen is an electronegative element and will always carry a negative charge. Now, it depends on its surrounding atoms about what charge it carries. In case of a hydroxyl group, the hydrogen carries a +1 charge. So, the opposite charge generated on the oxygen atom along with magnitude will be -1.
In the case of only oxygen atoms, we know that the oxidation number of oxygen is equal to -2. So, the charge generated on the adjacent atom of oxygen will be +2.
Thus, the oxidation state of phosphorus atom will be generated because of:
Oxidation state on phosphorous $= [2\times (\mathrm{P}-\mathrm{OH})+(1\times =\mathrm{O})+(1\times -\mathrm{O}\left)\right]$ oxidation states

Thus, the oxidation state of both the phosphorus atoms will be:
${\mathrm{P}}_{\mathrm{O}.\mathrm{S}}=2\times (+1)+1\times (+2)+1\times (+1)=+5$