Sorry, but I disagree. ERP is my life's work for more than 25 years and I can state categorically that is not " how most ERP systems are set up..."
These phones are not being manufactured to order. The manufacturer ships phones in bulk to the distribution center and, at that point, they should be pulled and shipped to orders FIFO-style. There is no excuse whatsoever for doing it any differently.
I will give a pass on the general possibility that shipments to different parts of the country might be made from different distribution centers, but each of those distribution centers should be processing orders in FIFO style.