I use these outdoors in Alaska and have found them to actually meet the manufacturer's claims. It's surprising how strong they are even when crammed in a pack or cargo pocket. They hold up well even with hard objects and square edges in cold weather and the seal is strong and waterproof. Much stronger and more waterproof than a ziplock freezer bag. I got mine from:
http://www.aeromedix.com/category-ex...rproof_Storage
Might be good for a cell phone bag. I use them for anything small and critical where I want waterproof and reusable storage (first aid, etc). Pretty reliable piece of kit.