Christie’s and Sotheby’s have long dominated the auction market for fine art. Now Phillips, the world’s third biggest auctioneer of international contemporary works, is about to open a new flagship salesroom here that it hopes could help challenge that duopoly.

The company, with auction rooms in New York and London, plus offices in eight other cities, has moved its European headquarters from Victoria, near one of London’s main railroad stations, to a 73,000-square-foot building at 30 Berkeley Square, in the heart of the wealthy Mayfair district