To share your entire screen on ClickShare from an iPhone or iPad, you can either use the ClickShare Mobile App or iOS native AirPlay (with supported ClickShare Base Units).
For more information on using the ClickShare Mobile App see KB 2950.
For more information on using the AirPlay with ClickShare see KB 3061.
To know if your specific Base Unit supports the use of AirPlay, please see What are the supported AirPlay features for my Base Unit? for a detailed overview of which Base Unit supports which AirPlay version.