With the use of the console you can establish a connection with your server. However, the console is only available when you are using a horizontal screen resolution with more than 992px available for the embedded console. If the resolution is below that value, a message will become visible stating "No console available". This can happen when you place several windows next to each other or if you use the 'zoom' function of your browser.
This same notification will also be visible on a mobile device. This is because the NoVNC console we use requires a physical keyboard to operate and does not function with an 'on screen' keyboard like your phone or tablet will use. This is regardless of the resolution, most mobile devices have a resolution which is large enough to display the console.
In a future release of NoVNC these problems with mobile devices might be resolved, but currently it is advisable to use an external connection. On most mobile platforms there are programs with SSH or RDP possibilities which you can use.