climb up vs ramp

climb up is not a noun while ramp is a noun.

Word	Noun	Adjective	Verb	Adverb
climb up	No	No	Yes	No
ramp	Yes	No	Yes	No

As verbs, ramp is a hyponym of climb up; that is, ramp is a word with a more specific, narrower meaning than climb up:

Other hyponyms of climb up include scale, escalade, mountaineer, ride.

climb up (noun)	ramp (noun)
	an inclined surface connecting two levels
	a movable staircase that passengers use to board or leave an aircraft
	North American perennial having a slender bulb and whitish flowers

climb up (verb)	ramp (verb)
rise in rank or status	stand with arms or forelegs raised, as if menacing
go upward with gradual or continuous progress	creep up -- used especially of plants
appear to be moving upward, as by means of tendrils	be rampant
	furnish with a ramp
	behave violently, as if in state of a great anger