What is the oxidation number of $\mathrm{P}$ in product when ${\mathrm{POCl}}_3$ is completely hydrolysed?

$POC{l}_3=x+(-2)+3(-1)=0,x=+5$ Oxygen has an oxidation state of -2 and hydrogen has a +1.

${\mathrm{POCl}}_3+3{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{H}}_3{\mathrm{PO}}_4$

So, oxidation state of P = +5