pile up phrasal verb ( see also ↑ pile )
1 . to increase in quantity or amount, in a way that is difficult to manage:
It wasn’t long before the debts were piling up.
The traffic starts piling up around this time.
The work has a tendency to pile up if I’m not careful.
2 . pile something ↔ up to arrange things in a pile:
tiny doughnuts piled up in a dish
⇨ ↑ pile-up