Where should I put my phone while it's recording?

If you can, we would say that the best place to keep your phone would be in an inner jacket pocket, where it sits on your chest.

If it's really cold out there don't stick it in an outside pocket, you don't want your phone to freeze. Also, your phone being cold can reduce GPS accuracy, and battery life too.

Just don't put it in your backpack. For your device to reliably receive GPS signal (necessary for Slopes to be able to record your day), it needs to be somewhere where it isn't too obstructed or the signals won't reach it.