Bond angle in `(PH_4)^+` is higher than that in `PH_3`. Why?

Bond angle in NH_4^+ is more than that in NH_3 .

Why bond angle of Phosphine (PH_3) is less than Ammonia (NH_3) ?

Bond angle in dimethyl ether is more than water.

C-O-C bond angle in ethers is higher than H-O-H bond angle in water through O is sp^3 -hybridisedin both the cases.

PH_3 has lower boiling point than NH_3 . Why?

The HNH angle value is higher than HPH, HAsH and HSbH angles. Why?