"'Body rise', if you interpret it literally CANNOT exist because, as you will soon notice if you stand in front of a mirror, it is impossible to lengthen the region of your spine from your coccyx to your skull short of lying down for 8 hours sleep (which apparently makes you grow about 1 cm or so, which gravity then robs back off you throughout the day as your spine recompresses), going into zero-gravity for a while (same principal) or perhaps the employment of some sort of medieval torture device such as the rack! The best you will manage, if you try, will be to shrug your shoulders (which is clearly not what is intended). Given the impracticalities of the formerly mentioned techniques during a bar of even the slowest foxtrot, then if you think logically about it, it can't have anything to do with your body or trunk as the name suggests."
This is not entirely true. Very few people habitually carry their spine aligned for maximum height, and encouraging students in that direction is very common habit of dance teachers.
It is true that the "mind game" effect on presence and performance is greater than they physical increase in height, but the increase in height is not zero.
This even applies, slightly, to body rise as a variable dance element. For example, the middle step of a lady's feather has no foot rise, but a lot of body rise - she need to be as tall as she possibly can be during the phase in which her weight is on her standing heel, because that's a point in time when her partner actually will have foot rise. Most of that is going to be in the leg (hopefully stopping just short of a locked knee), but some of it is going to be in keeping the trunk as aligned, and thus as tall, as humanly possible - and then some.