Breaking tasks into bite sized chunks, such as the steps of a checkout process is a well-established UX design principle. This principle is even more important for mobile designs because you don’t want to throw too much complexity at a user at any one time. Don’t just replicate the steps from a desktop site or app, because there is likely to be too much complexity when tackled on a mobile. Instead try to keep each step as focused and as simple as possible. Ideally each step should focus on one thing, and one thing only. This might result in more steps but will also result in a better mobile experience.