There's no operating rail between LA and Phoenix, freight or passenger. Union Pacific rerouted freight away from Phoenix decades ago, Amtrak followed suit, and the previously used rail line that connected LA and Phoenix is out of service. See https://en.wikipedia.org/wiki/Phoenix_Subdivision_(Union_Pac... and https://www.arcgis.com/apps/mapviewer/index.html

The US already has the best freight rail network in the world my many measures but you can't put every shipment on a train.

Do you think long haul trucking does not exist today? Use a train when you can, but that is not always an option.