Basically, if you have ever played Honkai: Star Rail and finished the Jarilo-VI's main story, then it'll be easier to explain for you:
I tried to recreate how this track plays in that game. Specifically, I'm talking about the phase switch at the final boss fight.

If not, then... uh...
Once the main assault phase track(1) is finished, it will either repeat, or switch to the alternative track(2). That's how BeardLib always handled this.
Now in this case, it'll only do the switch from (1) to (2), but it'll never switch from (2) to (1).