Question

show the formation of ion of phosphorus

Answer 1

the phosphorus atomic number is 15
it needs 3 more electrons to get stability and obtain octet rule.
therefore, it forms P-3 ion with lesser atomic radius and with 18 electrons, its charge is negative. 

Answer 2

The atomic no of phosphorus is 15
it needs to 3 more electrons  obtain its octet which is stable
therefore, it forms P-3 ion   with 18 electrons, it has a negative charge