Answer
$3$, $\pi$, $\frac{\pi}{4}$.
See graph.
Work Step by Step
1. Given $y=-3cos(-2x+\frac{\pi}{2})=-3cos[-2(x-\frac{\pi}{4})]$, we can find the amplitude $|A|=3$, period $p=\frac{2\pi}{2}=\pi$, and phase shift $\frac{\pi}{4}$.
2. See graph.