Definition of choose up:
(v) :
(idiomatic, intransitive) To select; pick, especially, to make a final decision on a selection or option.
(v) :
(idiomatic, intransitive) To form (sides or teams), usually for a game, by having two individual players choose their teammates.
(v) :
(idiomatic, intransitive, African-American Vernacular, slang) To choose (not necessarily fully consensually) to work as a prostitute for a particular pimp.