Comment by mjevans

I want to use the extremely simple and reliable direct interface and inexpensive cheap earphones and patch cables that I can buy in any reasonable electronics store for low markup. They are all passive components.

Adding an external sound card introduces variables outside of manufacture control, the quality, latency, and drive power all at the mercy of some random integrator.

My phone is easily thick enough to accommodate a 3.5mm port, and it can't be that difficult to waterproof such a jack, which should also make reasonable cleaning easy if it's ever required.