When you choose Dynamic Text in the layout, you're choosing Relative Scale, correct?
As you describe, when I do that, it gives me 1 inch equals x miles
You want inches = feet.
Click on the 'Help with dynamic text' link which will take you here: Modify dynamic text—Layouts | ArcGIS Desktop
and Ctrl+F "scale"
Look for the description about working with Relative Scale:
I followed that guidance, clicked the Scale button in the dynamic text window and changed the mapUnits to "feet".
Then change the text to whatever you want. For example, if you want '=' instead of 'equals' just change it.
Here's what my example looks like:
Hope this helps.