mushroom into (something)

To increase, expand, or grow into something much larger in size, scope, or scale than something was initially, especially in a short space of time. We started out as a small mom-and-pop shop, but the business mushroomed into a huge nationwide chain in just a few years! What was a minor talking point during the beginning of his campaign has mushroomed into one of the key issues of this election.

Fig. to grow suddenly into something large or important. The question of pay suddenly mushroomed into a major matter. The unpaid bill mushroomed into a nasty argument and, finally, a court battle.