Yes, it's still useful — just for a different reason than originally intended. The headphone cord port that these pockets were built around is largely obsolete now that wireless earbuds are the norm. But the core benefit remains: keeping your phone warm and protected from moisture.
Cold temperatures drain phone batteries fast, and an internal pocket sits close to your body heat, which helps prevent your phone from shutting down mid-mountain. It also shields your device from snow and sweat better than an outer pocket.
That said, if you don't ride with music or prefer keeping your phone in your pants pocket under your jacket, you won't miss this feature. It's a nice bonus rather than a must-have for most riders.