Thinking of the Pi0, I assume you would need 2 usb cables and a hub: 1 cable goes to Pi's power usb port, 1 goes to the other usb port for connectivity, then both cables joined through a hub to the phone's usb port.
May have been also that when you connected Pi to a power source it powered the phone too. I was using this system 10 years go with very cheap phone without OTG, so Pi was solution to this and other problems.