The research phase is where you immerse yourself in the project to get the background you’ll need to make design decisions later in the project. During this phase you will try to learn as much about your client’s business, objectives, users and competitors as possible.
The design phase is where you work out how what you are designing will work and how it will fit together. This phase will define its scope, its features and functionality and how it behaves.
The validation phase is where you identify whether what you came up with in the design phase actually works with its intended audience. This phase is typically followed by further rounds of design and testing to solve the problems you inevitably find when you test with users.