If you have a dedicated mobile site (if your main site is not a responsive design), you can make a mobile form by using the form appearance using the Form Layout controls to adjust the width of your form down to about 300px.
After the form is built and you've adjusted the width, you can then copy the form's embed code to your clipboard.
Finally, paste that embed code into the HTML editor on a Standard mobile page.
Note: You can adjust the visual look of the form on your mobile page by editing the properties of the embed HTML. Recommended adjustments include changing 'frameborder="1"' to 'frameborder="0"' to remove the border around the form, and altering the value of the height. This will depend on the size of your form, and may take some tinkering to get an exact number. The width attribute of the embed code should not need to be edited, as this is automatically adjusted based on the Form Width setting.