Currently, if you'd like to show the Olark chat box on the mobile version of your website, you'll need to enable the beta mobile interface.
Go to the Advanced configuration to enable it:
Give that a shot, and keep an eye out for even better mobile Olark in the future!
Still not seeing your website's chat box when testing from a mobile device? Make sure that "private browsing" is turned off in your device's settings. Olark only loads on devices that allow stored cookies.