That person is just holding onto it just in case the person that lost the phone irresponsibly decides to come looking for it. I jest. It is theft if the person that finds the phone doesn't take at least the basic steps in returning it, or at the very least leaving it where it is.
Sadly, I've found phones lying in malls from time to time, and I personally leave them right there.
Funny, but it'd be like saying the guy put his phone on the table at a cafe, and someone just came by and snatched it. If the Brinks truck left the money bag on the corner and drove off, and no one was around . . . .well 😉 I am sure they' love the bag back.
Yeah, but seriously speaking, it extremely irresponsible for someone to just leave an expensive phone lying around. It's theft and it does suck, but your friend was asking for it.
Tell him/her to wait for the iPhone 5!