Absolutely return to a big pile of MP3s. Just not for this silly bullshit reason. Control, privacy, and reliability matter. The carbon footprint of charging your phone does not.
Jesus Christ, it's like wagging a finger over using a Game Boy Advance to play Game Boy Color games. It's 5v instead of 3.3v! The letterboxing wastes power on black pixels! You're gonna burn through those AAs slightly faster!
I think one serving of tofu has more carbon footprint than a whole day streaming video.