For phase shift: $\phi = -tan^{-1} (\omega RC)$
				<br>
				As $\omega \rightarrow 0$:
				$$\phi \rightarrow -tan^{-1} (0 RC) = -tan^{-1} (0) =  0^{\circ}$$

				<br>
				As $\omega \rightarrow \infty$: 
				$$\phi \rightarrow -tan^{-1} (\infty RC) = -tan^{-1} (\infty) = -90^{\circ}$$