1i agree with aveek
c basically size of nitrogen is smaller than that of phosphorous which means charge density of Nitrogen>Phosphorous which means that repulsion is greater in nitrogen thus the reduced bond angle....hope u get it bro
4 Answers
1Nitrogen being more electro-ve than P , the bond-electrons are located more closer to the N in NH3 than P in PH3 . Hence in NH3 the electron-repulsion being more the bond-angle increases. hence Bond-angle in NH3 > Ph3
1
106well bond angle of PH3 is very very less than expected for sp3 hybridisation (93 degrees instead of usual 109 degrees)
see this for explanation:
http://targetiit.com/iit-jee-forum/posts/bond-angles-of-nitrogen-family-13162.html
specially the second reason