It might be "only a phone" to some people, but for others it's not. Also, perhaps people just don't trust others to handle their personal items with care. Everyone knows a fumblefingers. You hand them something, and they drop it. Or they mess around and break it.
I have some cameras. You could say "it's just a camera." However, I'm not going to let just anyone play with it. I don't let anyone touch my camera stuff except me.
Yeah, it's just a camera. But if I hand it to you, and you drop it -- are you going to pay $2500 to buy me a new one? No, you won't. You'll say "it wasn't my fault."
Perhaps rich people can afford a new phone all the time. I personally cannot. I got this Droid from my parents as a Christmas present. I was quite happy with my Razr, which I had for years, and still looks brand new.
As for my new phone, it now has sentimental value in it, because my mother passed away just before Christmas. This phone is the last thing she gave to me.
So in my case, everyone can keep their paws off.