If Project Linking is configured in the WebOffice 10.5 SP2 application configuration, the WebOffice mobile client offers an additional Projects button in the upper toolbar. After having pressed on the button, a drop-down list with all available (i.e. configured) projects will appear. Picking a project causes a project change in the same browser tab.

Projects in the WebOffice mobile client - tablet mode
In phone mode, the list of projects will open in a new browser tab.

Projects in the WebOffice mobile client - phone mode
Note: See chapter Project Linking for details about the configuration of project linking in WebOffice author.