Moving your body to generate power makes more sense for running low power sensors or some LEDs than charging an android or iPhone. It takes several watts to charge a phone and that should be a continues stream of power. I'll have to find the numbers to do the math for kinetic energy harvesters but it seems to me that the body movement activity to sufficiently charge a smartphone would be closer to vigorous dancing than casually shopping. A typical electric wheelchair motor is 250 watts so it uses roughly the power of 100 smartphones when operating.