If you enter 'make up' in a search engine you are mostly likely to find references to cosmetics.  As a verb, 'to make up' was also used when talking about applying cosmetics.  However, there are many other ways to use this phrasal verb.

I made a video explaining four different ways 'to make up' is often used:

http://www.enupgrade.com/speak-up/2014/7/23/phrasal-verbs-make-up

There are several other meanings that could be explored.  Where have you seen 'to make up'?