You need a 3-port OTG cable - one plugs into the phone, the drive plugs into the second port and the power supply (assuming it's 5 volts - the drive is powered from the USB port) plugs into the 3rd port. You should be able to use the phone's charger -the USB port can't put out as much as most chargers, so if it runs off a USB connection, it'll run off the phone's charger. (The phone won't be powered, so be sure the battery is fully charged.)