You can charge the phone in the headset by connecting a USB-C cable to the charging port at the bottom of the headset (Figure 1). It can be a convenient option because you do not have to remove the phone from the headset to do it. If you encounter any problems charging the phone this way, make sure of the following. You must be using the USB-C cable (Figure 2). You must have the cable plugged into a wall outlet, not a computer outlet. You must make sure that the connection between the phone and the headset is solid. It is also worth noting that there is no way to tell how much the phone has charged when it is in the headset. Although, you will hear a noise from the phone the moment you connect the headset to a power source, indicating that charging has started.
Figure 1: Location of USB-C Charging Port
Figure 2: Comparing USB-C and USB Cables