A thin volume rocker runs along the left edge of the phone next to the microUSB port. (laptopmag.com)
The left edge of the phone is home to a microSD slot and a microSIM slot, both hidden beneath and hinged door, and the right edge contains the power / lock button as well as a volume rocker. (bgr.com)
It's on the left edge of the phone, right under the volume rocker. (greenbot.com)