GoKawiilRemember the iPod? Those dedicated portable music players marked the next evolution of the Walkman and MP3 players. When Apple introduced the iPod Touch, it mimicked the first iPhone in look. So, it's not that much of a stretch to use an old iPhone like a makeshift music player. Wipe it clean of every app but your favorite music streaming services. Then stream while on a Wi-Fi network, download songs from a streamer you subscribe to or transfer music files you own. With the phone empty of everything else, you can dedicate the entire storage to music in nicely organized playlists.
Then, use it to play tunes at a backyard barbecue, on the beach or while camping, connected to a portable Bluetooth speaker. Bring it with you for commutes or travel for personal listening while using your primary phone for core purposes. The benefit is that you're not draining your primary phone's battery. Aside from music, an old iPhone could also be a portable gaming device using services like Apple Arcade or basic game apps.
Another idea could be to set it up on your nightstand with a charging dock or kickstand, permanently plugged in. Any iPhone with iOS 17 or higher works with the StandBy mode when positioned horizontally, which turns the screen into a bedside clock and wake-up alarm. If connected to Wi-Fi, you could play music once you wake up or even have Siri advise you of the current weather, traffic and your calendar and to-do items for the day.
On the go, set it up with a navigation app, hotspot it to your phone, then mount it on bicycle or motorcycle handlebars to use as a dedicated navigation device. While it doesn't have an eInk screen, you could also use an old iPhone as a dedicated eReader, downloading your favorite titles from an eReading app to read at home and on the go.