Even for a photo of less than 16Mpix resolution "original" and "high" are not the same thing. "High quality" is compressed. For the quality of most phone photos, and the uses they are generally put to, the compression won't be a problem for most people, but nevertheless it is not the original file.
If the image is > 16Mpix it will be scaled down to 16 Mpix as well as being compressed.
So if you select "original" I would expect that to be treated as "original" regardless of the number of pixels in the image.