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.