Here are a coule of those handlebar bags that you can wear off the bike:

http://www.teamestrogen.com/prodDT_1122.html

http://www.teamestrogen.com/prodDT_1188.html

I have Bontrager's version of that bento box, which I use for my phone, inhaler, pocket pack of tissues, and a couple of packets of Gu. I keep my jimi wallet and keys in my seat bag because the bento box isn't big enough for everything. If I'm walking away from my bike I just put the phone, wallet and keys in my pocket.

I don't have any problems with my phone (or anything else) falling out of the bento box, although you do need to put everything in plastic if it rains. But then the stuff inside the seat bag gets wet in the rain, too.