The experience of filling out a form in a mobile device environment is substantially different from filling out a form on a laptop or desktop. There is no mouse, or even (often) a Tab key to navigate between form fields. Big fingers and tiny options in popup menus make for a bad match. A form that might work fine in a full-sized browser may well be terribly uninviting and inconvenient in a mobile device.
Part of the solution to that challenge is that mobile devices often convert form fields to more accessible elements. For example, options in a select menu might display much larger when tapped, making it easier to make a selection.
The other part of the solution for making forms accessible and inviting in mobile devices is to implement new form fields, such as sliders (where visitors can choose from a range of values by sliding a thumb on a bar) or flip toggle switches (with easy to use "on" and "off" switch options) to make filling out forms...