are both tickets on UA or just the lax-eze part? If they are both on UA, you might get someone at PHX to book you direct to IAD and bypass LAX (unless you need the miles in which case, keep your routing). You'd need to check the flight schedule to see if this is doable but could be worth the request.
And if they are both on UA, OP should be able to standby for an earlier flight for no charge. (Availability required)
