I carry my cell phone in my pants. Like some others here I'm a big fan of the Wrangler activity pant from Walmart and it has a thigh pocket exactly the right size for my phone. It's a subtle effect but my phone weighs half a pound so it still reduces what I have weighing my pack down.
To save a little weight I got a unit with integrated cables and half the time I use a 5,000 mAh unit rather than the 10,000 size most folks carry. 5,000 is plenty for me for day trips and overnights, so why carry a bigger pack than I need?