Originally Posted by
qukslvr619
But how can you be standby on your first two segments? In that sense you would lose the confirmed seats.
You should request the standby for the earlier DFW-STL flight just after you arrive at DFW, presumably at the gate podium at your arrival gate.
That would not produce any issues. However, if you would like to stand-by right now, at SAN or at PHX, you would need to stand-by for any SAN-STL or PHX-STL combination, and to keep your original seats on the same flight, you must request stand-by on an itinerary where all the flights are different flights than those you have confirmed seats.