speak up vs utter

speak up is not an adjective while utter is an adjective.

Word	Noun	Adjective	Verb	Adverb
speak up	No	No	Yes	No
utter	No	Yes	Yes	No

As verbs, utter is a hypernym of speak up; that is, utter is a word with a broader meaning than speak up:

Other hypernyms of speak up include mouth, speak, talk, verbalise, verbalize.

speak up (adjective)	utter (adjective)
	complete and absolute
	without qualification; used informally as (often pejorative) intensifiers

speak up (verb)	utter (verb)
express one's opinion openly and without fear or hesitation	express in speech
speak louder; raise one's voice	articulate; either verbally or with a cry, shout, or noise
	express audibly; utter sounds (not necessarily words)
	put into circulation