What is the oxidation state of phosphorus in $HP{{O}_{3}}$

Hint: Oxidation state can also be called as oxidation number which describes the degree of oxidation
The degree of oxidation state can be either positive, negative or zero
Oxidation state includes loss of an electron or gain of an electron so that it can create chemical bond with the other atom
 $HP{{O}_{3}}$ is metaphosphoric acid. Identification of oxidation number of each element and total charge calculation helps to find the oxidation state of phosphorus.

Complete answer:
The oxidation number of Oxygen in $HP{{O}_{3}}$ is $-2$
The oxidation number of Hydrogen in $HP{{O}_{3}}$ is $+1$
The oxidation number of Phosphorus in $HP{{O}_{3}}$ is $+5$
The number of Oxygen in $HP{{O}_{3}}$ is $3$.
The number of Hydrogen in $HP{{O}_{3}}$ is $1$.
The number of Phosphorus in $HP{{O}_{3}}$ is $1$.
The Oxidation number of each element can be confirmed by total charge calculation
Total charge calculation of $HP{{O}_{3}}$:
It can be calculated by the addition of each element by multiplying the number of atoms and their corresponding oxidation number
There are 3 Oxygen, 1 hydrogen and 1 phosphorus. Therefore, $3O,1H,1P$
and their corresponding oxidation number are $-2,+1,+5$
$3O+1H+1P=3(-2)+1(1)+1(5)$$=+1+5-6=0$
Total charge$=+1+5-6=0$
From the total charge calculation, it is confirmed that the oxidation number of phosphorus in $HP{{O}_{3}}$ is $+5$
The degree of oxidation state in our case is zero

Note:
Therefore, the oxidation state of Phosphorus is $+5$ in $HP{{O}_{3}}$
Oxidation state can be identified by total charge calculation of each element
The term oxidation itself signifies the reaction between the oxygen and our substance either by loss or gain of electrons.