get on vs mount up

get on and mount up both are verbs.

Word	Noun	Adjective	Verb	Adverb
get on	No	No	Yes	No
mount up	No	No	Yes	No

As verbs, get on and mount up are synonyms defined as:

Other synonyms of get on include bestride, climb on, hop on, jump on, mount.

get on (verb)	mount up (verb)
develop in a positive way	get up on the back of
appear in a show, on T.V. or radio
grow old or older
get up on the back of
grow late or (of time) elapse
get on board of (trains, buses, ships, aircraft, etc.)
have smooth relations