LR Mobile only displays collections that you have specifically Synced with LR Mobile. There is a little arrow type icon to the left of each collection to Sync with LR Mobile. But I'm not sure you can sync more than one collection at a time. I don't know because I find LR Mobile to be a Bad Joke played on users.
I agree with Just Shoot Me, Lr mobile is a poor solution for what it is supposed to do.