${\mathrm{NH}}_3$ has a much higher boiling point than ${\mathrm{PH}}_3$ because 

${\mathrm{NH}}_3$ has a larger molecular weight

${\mathrm{NH}}_3$ undergoes umbrella inversion

${\mathrm{NH}}_3$ forms hydrogen bond

${\mathrm{NH}}_3$ contains ionic bonds whereas ${\mathrm{PH}}_3$  contains covalent bonds