Zero aperture control, poor depth of field, internal reflections, chromatic aberrations on the 0.5x, barrel distortion on main lens, poorly corrected vignetting.
Lateral chromatic aberration, barrel distortion and vignetting are easily corrected in software, which is why modern lens designs for digital cameras tend not to prioritize these aspects of lens performance. It is possible to disable lens corrections in the iPhone camera settings, so maybe this is what you were seeing.
