Why reaction between phosphorus and oxygen produces four atoms of phosphorus and five atoms of oxygen

Reaction between an oxygen and  a phosphorus will produce oxides of phosphorus.

Explanation:

Reaction between oxygen and phosphorus produces four atoms of phosphorus with five atoms of oxygen. Sometimes it produces two atoms of phosphorus and five atoms of oxygen and sometimes four atoms of phosphorus and six atoms of oxygen. It does so depending upon the availability of oxygen. The size of phosphorus atom  interferes with the ability to form a double bonds to the other elements, such as nitrogen, oxygen, etc.