> no reason it can't be on my phone and buzz my leg instead of my wrist There's a much higher density of tactile nerve endings in your wrist than in your thigh

> no reason it can't be on my phone and buzz my leg instead of my wrist There's a much higher density of tactile nerve endings in your wrist than in your thigh; even if you can reliably feel your phone vibrating in your pocket (I can't!), that's no guarantee you'd be able to discriminate finely enough for haptic feedback to be of use, especially since the phone's orientation in your pocket is not guaranteed.