The increasing order of the first ionization enthalpies enthalpies of the elements B, P, S and  F (lowest first) is:

The increasing order of the first ionization enthalpies enthalpies of the elements B, P, S and  F (lowest first) is $\mathrm{B} < \mathrm{S} < \mathrm{P} < \mathrm{F}$.

In general, the ionization enthalpy rises with increasing atomic number as we move from left to right in a period. As we move down a group, the ionization enthalpy decreases. 

Because P$\left(1s^{2}2s^{2}2p^{6}3s^{2}3p^3\right)$  possesses a stable half-filled electronic state, it has a larger ionization enthalpy than S. Ionization energies are increased in sequence.