add to vs increase

add to is not a noun while increase is a noun.

Word	Noun	Adjective	Verb	Adverb
add to	No	No	Yes	No
increase	Yes	No	Yes	No

As verbs, increase is a hypernym of add to; that is, increase is a word with a broader meaning than add to:

add to (noun)	increase (noun)
	the act of increasing something
	the amount by which something increases
	a change resulting in an increase
	a process of becoming larger or longer or more numerous or more important
	a quantity that is added

add to (verb)	increase (verb)
have an increased effect	become bigger or greater in amount
	make bigger or more