On my USA keyboard, the shortcut key is:

ctrl-`

(Control-backquote, the key to the left of the 1/! on the top row)

You can also add a button to the toolbar to toggle this with a mouse
click...

Right-click a blank area of the toolbar and select Customize from the popup
menu.

Select the Command tab on the dialog box that appears.

Select Tools in the Categories list and then scroll down in the Commands
list until you find Formula Auditing Mode

Click and drag the Formula Auditing Mode icon to some place on one of the
tool bars and release the mouse button.

The Formula Auditing Mode icon should now appear on the tool bar. Close the
Customize dialog box. Whenever you click this icon, the formula display mode
should toggle.

Rick