Nitrogen forms N₂ but phosphorous do not forms P₂ but it exist as P₄ the reason for this is:

Multiple bond is formed easily

Triple bond present between phosphorous atoms

$\mathrm{p\pi }-\mathrm{p\pi }\text{ bonding is weak in phosphorous }$

$\mathrm{p\pi }-\mathrm{p\pi }\text{ bonding is strong }$