Glad the article was relevant for you!
To your questions, the phases of strength should proceed one at a time, generally speaking. I’ll often prescribe strength in overlapping fashion, such that when an athlete advances to a new phase, we use elements of the previous phase as a second strength session of the week. For example, when someone proceeds from a Foundational workout to Max Strength, I’ll put the Max workout on a Tuesday and then on Thursday or Friday we’ll do a core workout and incorporate some elements of the foundational work, just to keep touch with it.
I especially like this method when someone progresses to M.E. training or are in the competition period. In those cases I’ll still prescribe a max strength session in the week, largely to serve a recovery function, because the max format does not elicit extensive-type fatigue the way M.E. or higher-rep workouts.
Re: how long each phase lasts, that’s really dependent on the athlete. Typically I’ll watch the progression and get feedback on how they’re feeling – if a Foundational workout continues to provide sufficient challenge, I won’t move them forward into max strength. With M.E., depending on the format you use, the gains will continue to build over many, many weeks (I’ll often keep folks on it for 12+ weeks) so you really have to monitor how the rest of the training is happening amidst it, how recovery is going, where you are in relation to key objectives, etc. Like so much of this stuff, the answer is “it depends”!