"Once Phase 1 ends and Phase 2 begins, any Balloons that were donated past the previous goal will be subsequently added to the new goal!"
That sounds as if the target will be increased by the number of balloons donated in excess of 350 million in phase I. In other words, if phase 2 goal is intended to be 700 million, and 400 million are donated in phase I, the excess of 50 million will be added to the goal, making it 750 million.
I hope it means that any balloons that were donated past the previous goal will subsequently be counted towards the new goal.