JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I just tried on several phones, and It is not showing those fields that are hidden. So, working as expecting. Can you please let me know on which device did you try?
I noticed that option 'Responsive form' is not turned on, so you should turn it on since you want to run it on the mobile devices as well. You can do that by going to Preferences in Form builder and just turn it on.
I'm working on an Iphone 6s Plus.