Please help on following:

Show if $\displaystyle m>1$ then $\displaystyle a^m \equiv a^{m-\phi(m)}(mod \ m)$ for all natural numbers $\displaystyle a$.

Basic Euler function is this $\displaystyle a^{\phi(m)} \equiv 1 (mod \ m)$ but how to build it up in order to answer the above question?

Thank you