stack vs stack up

stack is a noun but stack up is not a noun.

Word	Noun	Adjective	Verb	Adverb
stack	Yes	No	Yes	No
stack up	No	No	Yes	No

stack (noun)	stack up (noun)
a large tall chimney through which combustion gases and smoke can be evacuated
a storage device that handles data so that the next item to be retrieved is the item most recently stored (LIFO)
a list in which the next item to be removed is the item most recently stored (LIFO)
an orderly pile
(often followed by `of') a large number or amount or extent

stack (verb)	stack up (verb)
arrange in stacks	arrange into piles or stacks
load or cover with stacks
arrange the order of so as to increase one's winning chances