Amongst walkers and climbers they're known as 'water bladders' or 'platypuses' after a popular brand, and the ones that come in their own little harness are often seen as a gimmick xD But they're invaluable when walking and most rucksacks come with a suitable pouch and hole for the hose. I find that I drink way, way more when I can take small mouthfuls regularly than when I have to chug down half a litre at once.
This is a CamelBak bladder in its own little harness. Sounds like the kind of thing that would be good for you - you can slip your phone in there too.
This is a Platypus :) It's basically a bag, a house and a mouthpiece.