I use my jersey pockets, but, I'm not stuffing a tool or a tire in there. LOL
And I sweat.. a LOT and putting my phone in there is a recipe for disaster.
I checked and what I am using is the Timbuk2 Bicycle Seat Pack (Medium). The 'main' problem I have with it is the zipper goes around the top edge and when the pack is fastened tightly against the saddle, you have to pry the pack down to open the zipper.