The focal length is just for exif fun. The aperture value lets the camera decide which AF sensor to use and does a correction of exposure.
Your understanding of AF is partly correct. The camera doesn't drive the lens to the phase difference=0 but to an adjustable phase offset value which is send form the lens.
Your understanding of AF is partly correct. The camera doesn't drive the lens to the phase difference=0 but to an adjustable phase offset value which is send form the lens.