Someday in the future, I'm convinced we will look back at workout leggings and laugh at the way that they were designed with one itty-bitty slit pocket hidden beneath the waistband. The same way that Victorian side-saddle skirts and Shape-Up sneakers seem archaic and impractical now, these too will become relics from the past.
Unless you are a descendent of Stuart Little or an American Girl doll, there is no way that all of your belongings can fit inside of a one-inch square pocket sewn into skin-tight fabric. You need a deep side pocket so you can forget about your phone, carry your keys, and maybe have room for a snack or something. Minimalism be damned, sometimes you need to schlep.
The good news is that you can find workout leggings with big 'ole pockets if you need them. Ahead are some leggings that are as utilitarian as a pair of cargo pants, but sleek enough for any workout.