When you resize the page, the form should resize together.
On mobile view you only can see half of the form, would be perfect if the form could resize to 100%.
Objects loaded via an iframe cannot be made responsive if the content from the iframe is not responsive.
There is no way you can change the contents from another domain in an iframe. Unless you have direct access to the form (meaning you can change the source code of the infusionsoft form), there is no way to this. Iframes are very limited in what they can do…