Running 5.6, I downloaded the "Foundation" theme to use as my Mobile Theme. I have another theme as my "primary" theme which works fine on a desktop, but it's not responsive. So I downloaded and installed Foundation Theme and selected and saved it in the are below the themes where it says "To use a separate theme for mobile browsers, specify it below."

But when I go to my website on a phone or tablet, the theme is my regular non-responsive theme, not the "Foundation" theme I have for the mobile version.

Do I need to do anything else to activate it?