Help with a infinite geometric series

My professor wants us to solve this infinite series in terms of $\phi$ and i. However, I have not worked with infinite series, or series in general, in several years. He mentioned using the geometric formula but I am not sure how to apply that here. Could someone help me start this?

$\sum_{k=i+1}^\infty \phi^{2k} (\phi^{-1} - \phi^{i})^2$ given $|\phi| < 1$