The only consistent domestic Flagship routes are JFK-LAX/SFO and DFW-Hawaii. Perhaps we'll see MIA-LAX come back in the off season. I also live in PHL, but the most I have gone out of my way for a lie flat product to LAS when there wasn't a widebody on the route was to go PHL-LAX on one and then do the 40 minute hop on a narrowbody. But even then it wasn't flagship service. It was just a nice seat without the casper bedding.
I've flown PHL-LAX-LAS a number of times. I used to do it regularly pre-COVID when there was a 4PM PHL-LAX flight on an A330.