Let be $\phi$ the Frobenius morphism, why $1-\phi$ is separable?

Question

Let be $C$ an elliptic curve defined over $\mathbb{F}_p$. We know that the Frobenius morphism $\phi:C\longrightarrow C$ is inseparable, i.e, $K(C)/\phi^*K(C) = K(C)/K(C)^q$ is an inseparable extension.

How can i show that $1-\phi$ is separable?