The hydrides of group 15, 16 below the 3rd period, follows Drago's rule. The rule states that due to a large energy difference between the atomic orbitals, these compounds do not exhibit hybridization. Thus, PH3 will not exhibit hybridization and here the bond formation takes place due to the overlap of pure p-orbitals and s-orbitals. PH3 has a lone pair on the central P atom, which is absent in PH4+. Thus in PH3, there will be bond pair - lone pair repulsion and this is the reason why the bond angle in PH3 is less than that of PH4+.