It helps to question yourself now and again. I did. This is interesting to me, and I am not too proud to say I neglected to give this a good hard look until fairly recently when it occurred to me that Phases can be, to some extent, compartmentalized and simultaneously co-dependent.
Directly from a PMI-affiliated content page with a bunch of worthwhile reading:
I really wonder if this is saying that 80 something percent of IT professionals are running Scrum, because I would have a hard time believing that, but regardless of the context the statement itself is noteworthy. A lot of the “Scrum” responses are probably Scrum-ish (iterative or having standups most likely) and TDD can reside within Scrum or Iterative, so it isn’t a knockout punch graph but I still like it. Today. 
Best,
Josh