  We report a systematic quantitative evaluation of parametric amplification
gain of magnetization dynamics in ytirrium iron garnet
($\mathrm{Y}_3\mathrm{Fe}_5\mathrm{O}_{12}$) thin disk via a.c. spin pumping
and inverse spin Hall effect. We demonstrate its signature phase-dependence
where amplification and attenuation occur every $\frac{\pi}{2}$ phase shift of
the input signal. The results also show the pump-power dependence of the gain
that is explained well by our theoretical model. Finally, the optimal
conditions for the amplification is investigated by measuring the magnetic
field dependence, where we find the highest gain of 11.4 dB.
