To make a print screen on an iPhone5, I use both hands, even though I’m not touching the screen at all.
I use my right hand to hold the device, my thumb on the smooth circular dent that is the home button. The rest of my fingers I use to exert pressure on the back, which I even out with my thumb, to hold it steady. My left hand I place around the top of the device, my index finger resting on the slightly protrusive elongated shape on top.
I Now simultaneously press the home button and the sleep button, (normally used to put the device to sleep), the buttons harmoniously produce two gentle clicks, the screen softly flashes white and I know a copy of whatever was displayed there a split second ago is patiently awaiting me in my camera roll.