Thanks for following up Erin!
I just checked your site on my mobile device (android) and simulating the breakpoint in the browser and I get the same result: the menu (blue bar) in your theme is overriding the submit button for filter so you can’t actually submit the filters.
Try adding this CSS code to your theme (or child theme) styleshhet or via Simple Custom CSS plugin:
#tribe_events_filters_wrapper {
z-index: 1001!important;
}
Please let me know if it works for you,
Best,
Nico