Answer
Nitrogen must obey the octet rule because it does not have a d orbital to accommodate as many fluorine atoms as phosphorus does.
Work Step by Step
The electron configuration of N is $1s^{2}2s^{2}2p^{3}$, so it can form 3 bonds due to the 3 unpaired electrons in the p orbital.
The electron configuration of P is $1s^{2} 2s^{2} 2p^{6} 3s^{2} 3p^{3}$. Although it does not have d orbital in its ground state, it can readily form 5 bonds because one of its 3s electrons are promoted, allowing for $sp^{3}d$ hydridization.
