Between $\text{NH}_3$ and $\text{PH}_3$, which is a better electron donor and why?

Question

$\begin{array}{1 1} NH_3 \text{ is the better electron donor because the lone pair of electrons occupies the spherical s orbital and is less directional.} \\ NH_3 \text{is the better electron donor because the lone pair of electrons occupies the} sp^3 \text{orbital and is more directional.} \\PH_3 \text{ is the better electron donor because the lone pair of electrons occupies the} sp^3 {orbital and is more directional.} \\ NH_3 \text{is the better electron donor because the lone pair of electrons occupies the spherical s orbital and is less directional.}\end{array}$