The AirPods come with a charge case that holds 24 hours of juice. If you manage to end up in a scenario where your phone is out of power, your AirPods are out of power,
and the AirPod case is out of power, that would be a fairly impressive bit of poor planning.
Besides, you can charge your phone and your AirPods at the same time, you just need to have two outlets (or two USB ports) and two cables.