By the property $\phi (n) = n.(1-\frac{1}{P_1}).(1-\frac{1}{P_2})......(1-\frac{1}{P_n})$ $m = \phi(P^k)$ $ = P^k (1-\frac{1}{P})$ $ = P^{k-1} (P-1)$

So answers should be D