What is the focal length of the iPhone 7's camera when accounting for video cropping?
On the iPhone 6, I have found the video crop with stabilization activated to be 1.1x tighter than a still photo with stabilizer deactivated. The field of view goes from 63.9° to 58.1°, diagonally. The effective focal length changes from 4.2mm (29.3mm on full frame DSLR) to 4.6mm (32.3mm on full frame DSLR).

If you overlay a still image from the video footage and align it to a photo from the same position, you can see this crop in action.