For a road bike nothing is better than a BENTO BOX. I also use the Box for my digital camera. Note the photo show only the small bag. The large, like mine is longer, easily fits keys and a a cell, or a digital camera.

Here's a link: http://www.totalbike.com/items/tni_b...large_xagc.htm

For the MTBike, I put the phone in my Camelbak using one fo the side vents but word of caution. A friend of my fell back into a stream and the phone, in the Camelbak, got covered with mud. Probably a good idea to use a baggie to cover.