Our starting point for design is longevity, which means making our devices more repairable, a very different approach to the electronics industry standard. To support maximum longevity and because of the IP rating, Fairphone 4 does not feature a headphone jack. In the end, it comes down to how we make a product that lasts for at least five years. We needed to eliminate as many vulnerabilities as possible, and the headphone jack is subject to dust and water ingress over time.

Again, you might disagree, you might know better, I don't know. But this is their motivation when it comes to longevity and hence sustainability. To me, it seems a reasonable idea: if the jack helps reducing the consumption of batteries in headphones but decreases the lifespan of the phones, it seems a bad tradeoff.