You can play MP3 files on an iPhone using four methods: the Files app for direct playback, Apple Music to sync files from a Mac, third-party apps like VLC for more features, and cloud storage services ...
I have a USB version of the Rio ONE MP3 player, and up until now it's been working fine. I used to use my old Mac to manage the songs, (since Windows required me to use RealJukebox to do it, whereas ...