And sometimes to not think. Taking a walk is a great way to clear ones head.

but sometimes I need a little burst of the phone/music to serve as a distraction and force me to unplug from the hard problem that i'm fixated on. once i've successfully started thinking about something else, phone/music off and let the productive mind wandering begin

I find that even if I use my phone while walking I will eventually stop paying attention to the phone.