On desktops, long forms are pretty normal. We've all seen registration pages and e-commerce ordering processes. The longer the form is, the greater the tendency to try to break them up into smaller, more logical pieces. This is usually done in a couple of ways:
Leave it as a full page, but inject enough whitespace and grouping that it doesn't look quite so intimidating
Either physically break the form into multiple pages or use show/hide techniques to accomplish the same thing
Neither of these approaches makes a lot of difference with regards to task completion. Either way, both methods are particularly unfavorable strategies within the constraints of mobiles. As a rule, users dislike filling out forms, so the best things we can do to increase success are:
Completely eliminate all optional fields
Reduce the number of required fields as much as possible (get vicious about it)
Pre-fill elements with reasonable defaults
Validate fields immediately instead of waiting...