1. Since Lax to Las is a domestic 2 cabin aircraft you won’t be able to use Flagship check in unless you have a concierge key status. So you will need to go to priority lane, not Flagship.
2. Usually lax to las is departing from terminal 4.
while you are in Uber to the airport just google “AA2249 flights status” and you will confirm what terminal is that if you want to be sure.