Ionization energy is defined as the minimum amount of energy required to knock out the electron from valence shell of an atom.
Trends in Period:
Ionization energy increases from left to right across the periodic table. This is because from left to right along the period the nuclear charge increases and the number of shells remain constant.
Trends in Groups:
Ionization energy decreases from top to bottom along the group. This is because down the group the number of shells increases and hence, the shielding effect increases shielding the valence electrons therefore, valence electrons are easily knocked out.
Conclusion:
So, we can conclude that elements at right to Phosphorous and above Phosphorous will have greater Ionization energies as compared to Phosphorous. Examples,
At right to Phosphorous;
Sulfur
Chlorine
Argon
At the top of Phosphorous;
Nitrogen
Oxygen
Fluorine
Neon