One thing sibling comments miss is how you can offer a jack & them, as a user, can still use whatever style you want & disregard the jack. It’s a cheap part that takes up some volume but not enough to force an entire redesign. But when manufacturers remove the jack, you are forced users into consuming either the wireless earbuds (that they all ‘conveniently’ sell branded) or cosuming a dongle which takes up the one charging port, are unruly in a way that puts additional stress on the port & make the wires hang awkwardly. Almost all other gear with audio that isn’t a modern smartphone includes the jack which means you can’t bring your existing gear—or it starts prompting every apparatus to start adding Bluetooth capabilities which includes the latency, flakiness, slow pairing but also the security & fingerprinting issues of keeping devices with Bluetooth always on in the first place. Even with replaceable batteries, you still need microcontrollers & firmware delivery.

That is to say, if Fairphone cared about sustainability, they can offer a better earbud on repairability (pressing doubt on the frequency-response curve tho), but they should still be offering a jack on their phones since wired headphones/IEMs are a more sustainable (& private & secure) personal audio option.