JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
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The jotform form's by default already support mobile browsers. Just create the form and it should be usable already when on mobile phone browsers.
I also recommend checking the user giude on -How-to-make-Forms-Mobile-Responsive
Adding the Mobile Responsive Widget on the form will also allow it to respond on mobile browsers even when the form contains custom component.
Please let us know if you need further assistance.