Question

Why is melting and boiling point of ammonia is higher than phosphine

Answer 1

HEY  THERE........

Although PH3  is a larger molecule with greater dispersion forces than ammonia.  NH3 has polar N-H bonds leading to strong hydrogen bonding . this is the dominant intermolecular force and results in greater attraction between NH3 molecules than there is between PH3 molecules

HOPE YOU UNDERSTOOD ............