I figured it out.
Add "container" class to the form classes
1. Open the form
2. Go to Settings 
3. Customize HTML
4. Enter "container" in the Form Classes input
Add custom CSS to Form style
1. Click on "Styles" under Formidable in the Wordpress navigation
2. Select your style
3. Click on the "Custom CSS" tab
4. Enter the CSS below in the Custom CSS textarea
 
.container {
display: grid !important;
}
@media only screen and (max-width: 428px) {
#frm_field_57_container {
grid-row: 1;
}
#frm_field_68_container {
grid-row: 3;
}
#frm_submit {
grid-row: 2;
}
}