iPhone compatible

I'm not sure what you mean by "compatible", JotForm forms can easily be used on any device as long as it has a web browser and an active internet connection. You just need to provide your users with the direct for link found under the "Publish" wizard, or you can embed it to your website.

If what you are referring is to how to make the form mobile responsive, then please do follow this guide: https://www.jotform.com/help/322-How-to-make-mobile-friendly-forms-on-JotForm 

I hope that helps.