Correct, the interface between the phone and the headset is the charge port, but there is an additional port on the Gear VR itself to allow for charging while being used.

The original Gear VR ("Innovator edition") could not be charged while used though if I remember correctly.

The person I responded to was complaining that the rift alternative (a phone with appropriate lenses) had limited time usage due to relying on a battery. Most phones can run indefinitely by hooking them up to an external power source, obviating one of the poster's concerns. Additionally, you could augment the phone's processing power through a high-speed interconnect (like the USB cable that also supplies continuous power).

Phones get very warm when you charge them while playing 3D games. I doubt you would want to have that much heat with an enclosed headset for very long. Unless you can get a lot of ventilation without letting light in.

FYI the person you were responding to was me, and I wasn't complaining.