If you're referring to the taskbar (where the Windows logo/start menu button usually resides), VoiceAttack is shown there by default.
If it's not shown in the taskbar, but shown in the system tray, you have enabled the "Minimize to System Tray" option on the "General" tab of the VoiceAttack options window.
However, clicking the system tray icon should also bring up VoiceAttack's main window.
Note that windows/applications that minimize to the system tray should not be minimized or restored using the "Perform a Window Function" action, as minimizing to the system tray is not actually a Windows feature and applications manage that state internally by showing a system tray icon and hiding their own window. Forcing the window to show or minimize can desynchronize that internal state (this is a Windows limitation).