If you are seeing a material battery drain from the iPhone's Motion Calibration & Distance setting, turn it off. Apple does not reveal how that is used in the watch calibration, because the setting pertains to the phone's M7 or M8 chip. So, maybe the phone is what does the total calibration and then feeds the stride factors to the watch.
Anyway, since it is a calibration setting and not essential for all ongoing use, you can turn it off if you are comfortable that the watch is calibrated the way you like it.