The details of a given UX design process will depend on a number of factors, including the project, the client, the budget, the deadlines, and the skills of those doing the work. Additionally, UX embraces user feedback and testing, making it synergestic with Agile development principles and the Lean Startup movement.
Core UX values, such as communication, evaluation, and iteration create considerable overlap between phases. As the design team learns more about the problems being solved, the audience, the stakeholders, or the constraints, it is often necessary to revisit some of the research undertaken, get additional user feedback, or try out new ideas.
When it comes down to it, I break the UX design process down to 3 phases: Research, Design, & Validation.