Okay, I have checked all likely fuses (most likely being the 20A "power SW" fuse), and all are good. Furthermore, I discovered that the USB power is not actually dead. I can power a small USB fan from the very same USB port! Yet my phone will not charge when plugged into this port, it will actually discharge faster than being left unplugged. There is nothing wrong with the phone, the same behavior occurs with my wife's phone.
Is there anybody who understands USB that can shed some light on this problem? For example, how much voltage and current can the USB port in the Leaf deliver? If I know that number, I can get on an Android forum and ask what is the expected charging behavior under those conditions.