I know some lower level RFB players (circa $600 per hand/ 4 hours per day) who have gotten the Phantom transfers at Wynn. It's really the luck of the draw and can't be reserved at that gambling level.
The Mansion at MGM also has a few Phantoms. According to my Maybach driver over a year ago, they're supposed to be getting Park Ward editions. I doubt that's going to happen or if Rolls will even make a Park Ward of the Phantom.
Caesars and The Venetian each have a Phantom in their fleet.
For the record, the only reservable Phantoms to non gamblers available in Vegas are through CLS Worldwide and transfers for The Mansion.