Bubble refers to Hallowed Ground.

It's called Bubble because it's essentially a copypasted ability from WoW that Paladins had at very low level, creating a golden bubble around themselves that made them impervious to all harm and mechanics for 8-12 seconds (depending on level). Its most notorious use was the ability to Bubble and then use your Hearthstone (10 seconds cast time) to teleport back to safety.

That said, Yoshi-P confirmed (not just in the recent newsletter) that a party that uses nothing but different jobs built its limit faster, and it's pretty easy to notice if you ever do it too.

Try getting a Coil group together that looks something like:

PLD WAR, SCH WHM, BLM BRD MNK DRG.

You'll notice how quickly the limit break bar shoots up compared to normal.