I pretty much only wear spandex Capri's and pants when lifting at the gym. I need my phone with me while strength training for music not for looking at FB between sets;) I've seen workout pants with phone pockets but most don't have them. Armbands don't work for me, they always fall off and not super fast to pull off and on. That leaves me sticking my phone in my bra. It's common practice for many gym going girls. It's convenient and doesn't fall out. However it gets sweaty, I'm sticking my hand in and out of my shirt(not classy) to switch up the music and my brothers girlfriend yells at me about boob cancer.
I cut and stitched on a stretchy pocket to the side of all my gym pants. I'm all fixed up! It's super easy to pull my phone in and out, the stretchy pocket keeps my phone from moving around and doesn't get in the way of my moves.