Researchers have built sensors that generate an electrical signal when you touch and release them. How much charge everyday swipes could add to a phone battery is a separate engineering question.

Fun idea, and it's been built, just with tiny numbers. The tech is called a triboelectric nanogenerator (static from touch, basically). - 2013: a clear film on a smartphone screen made enough from normal tapping to light 3 LEDs (about 1 µA per cm² current). - 2015: a palm-tapping harvester with p...

The replies here say tiny numbers, so here is the figure. A phone battery holds about 54 kJ; a screen-sized harvester at a generous 5 mW needs roughly 125 days of continuous swiping to fill it, while the display above it draws a watt. The version worth building is a phone that needs a thousandth of ...