A phase detection autofocus (PDAF) algorithm iteratively estimates the phase shift between the left and right phase images captured in an autofocus process and uses it to determine the lens movement until the estimated in-focus lens position is reached. Such phase images have been assumed to be equivalent to a two-view light field. If the assumption is true, then the phase shift between the two phase images can be obtained by stereo matching or similar techniques. In this paper, we argue that it is a wrong assumption and provide insights into the distinctions between phase images and two-view light field from the autofocus perspective. We also support our argument by conducting an experiment to show that both stereo matching and optical flow result in inferior PDAF performance than the phase correlation technique and the AF-Net technique that specifically target phase images.