In ammonia `(NH_(3))`, the molecules are involved in the intermolecular hydrogen bonding on account of the polarity of N-H bonds. But the same is not possible in molecules of phosphine `(PH_(3))` since the polarity of P-H bond is negligible as compared to N-H bond. This is due to lesser electronegativity of phosphorus (2.1) as compared to nitrogen (3.1). Therefore, boiling point of ammonia is more than that of phosphine.
