Chapter 3 of the PMBOK states that process groups are not the same as project lifecycle phases. It states that all process groups could be conducted within any phase. For example clinical trials may be part of the execute phase of a project, but it would require all the process groups. You would need to plan the trials, initiate the trials, execute the trials, monitor and control the trials and close out the trials. So project phases are very specific to both the project and the industry (medical device). Whereas the process groups are universal and can and should be used for each step of the project. What are some other areas unique to medical devices where we may use all the process groups throughout the project lifecycle? Product Risk Management is another great example of this!