I think the phone didn't broke, but they ended up losing contact anyway.
In chapter 22 you can see how she tries to call her but the number didn't exist anymore.
Maybe next month there will be a new panel where Satsuki and Akira are at the altar in wedding dresses :nyoron:
I know the story wasn't as much for GL's romantic sense but I still don't feel like Komachi deserves the position of "always living by your side" more than Akira.