stack up phrasal verb ( see also ↑ stack )
1 . stack something ↔ up to make things into a neat pile
2 . informal used to talk about how good something is compared with something else
stack up against
Parents want to know how their kids’ schools stack up against others.
3 . if a number of things stack up, they gradually collect or get stuck in one place:
Traffic stacked up behind the bus.