Mobile layout is a different theme?

Hello, I have a client who is using the Mantra theme. I needed to add some custom code to the theme’s functions file. That was successful. The problem is that the site seems to load a different theme on mobile. I don’t see this in the settings as an option. What might I be overlooking?

Specifically, the addition to the functions file is to allow HTML when rendering a google sheet. On one page, I have some rendered spreadsheets.
Here is the page: http://ovba.org/ogden-valley-businesses-2/

When that page renders on mobile, it seems to no longer use the same functions.php file.

Website: ovba.org/ogden-valley-businesses-2