Keep all your bike repair and travel accessories in one place. Small compact enough to fit in your back jersey pocket, yet big enough to carry multiple emergency items.
Throw away your under the saddle bag, and keep your bike clean and pure. Rule #31 of Velominati states "Spare tubes, multi-tools and repair kits should be stored in jersey pockets". So this is a means to de-clutter and keep your phone safe and usable on the bike.