There should not be a design phase without prototyping first. It is at this point where you can play with ideas and concepts and give valuable feedback to shape the final design.
You will be able to experience a simulation of the final interaction with the interface to check its usability rather than simply reading a product description. Given that interactions need to be modeled, this stage involves coding so that users can experience content and interactions with the interface.
During this stage, we will also work on mockups which are a design representation of your app. It helps you visualize the content of the app and the basic functionalities in a static way. it is the perfect feedback-gatherer to review the visual side of the project.