Stephen Hung's purchase surpasses the 14 Phantoms bought by Hong Kong's Peninsula Hotel in 2006.
Hung and Rolls-Royce executives signed the deal yesterday at the company's Goodwood factory in England.
The Extended Wheelbase Phantoms will be used to chauffeur guests at Hung's "ultra-luxury" Louis XIII hotel, which is scheduled to open in early 2016.
Rolls-Royce said two of the cars will be the most expensive Phantoms ever commissioned but it did not disclose prices or the order's total value.