You can't pop your smartphone in the wash, but there are various products out there to keep it clean. You can sanitise your mobile phone with a sterilisation box, screen wipes or a special cleaning fluid.
When cleaning the sensitive touch display, be sure to use a screen cleaner or sanitiser designed specifically for mobile phones. Wipe the display and other exterior surfaces with a soft microfibre or glasses cloth. It is also worth cleaning the phone case every once in a while. Depending on the material, it may be possible to rinse it under running water.