Yeah I also wonder what a thief would do with it? Maybe the recycle value is enough for her? Or she gets it to a store where they don't check and recycle parts?
While walking and without alerting the person you just bumped into to the fact that you just took their phone? More realistically, a well-prepared/tech-savvy thief could just drop the phone into a Faraday bag in their backpack/pocket, or alternatively just turn off the phone!
Fortunately, the one that my friend encountered didn't do any of that.