They are moving from London's Victoria to 30 Berkeley Square, which Phillips say will become their "European flagship location, mirroring the sale room, exhibition areas and offices in New York on 450 Park Avenue".
It will be launched next month with a sculpture exhibition and an inaugural sale, the Contemporary Art Evening Auction, on October 15.
Multi-purpose exhibition spaces will occupy the double-height ground floor, first floor and lower ground floor, with Phillips taking a total of 31,000 sq ft in the 73,000 sq ft building. That inaugural auction will take place into the lower ground floor. Also double-height, it has been designed to accommodate exhibitions, auctions and private events and houses "private sky boxes overlooking the auction room", for publicity-shy bidders.
The move follows the appointment of Ed Dolman as chairman and chief executive of Phillips earlier this year, and recent Phillips office relocations in Europe including a Parisian office and exhibition space on Rue du Bac and a new Berlin office on Kurfürstendamm.
ATG reported in April how Mr Dolman, former Christie's chief executive, was joining Phillips after quitting as executive director of the Qatar Museums Authority, a job he took up on leaving Christie's in 2011.
While Phillips focus now on contemporary art, photography, jewellery and design, at the time of Mr Dolman's appointment they said: "He is primarily focused on the execution of an aggressive growth strategy for the business which will include a move into categories not currently offered by Phillips, while continuing the geographic expansion of the business."
When asked by ATG for more detail on what the new saleroom could offer, a Phillips spokesman said: "We are not able to say at this stage what these categories are but will say that whatever is added will complement our existing offering in the contemporary, luxury lifestyle sector."
Watches have been mentioned as a new category.
Regarding their Victoria premises, the spokesman added: "We are in discussions with a candidate to take over the lease of Howick Place."
Part of the expansion has seen the appointment of two new specialists in their Modern and Contemporary Editions department in London.
Anne Schneider-Wilson has joined Phillips after 13 years of experience within the art industry, most recently working for the Paragon Press with Charles Booth-Clibborn, one of the leading publishers of contemporary prints. Prior to this, she worked in the Sotheby's prints department for seven years.
Ross Thomas has been appointed specialist in the Editions department based in London, having previously worked for Dreweatts and Bloomsbury Auctions, where he was in the prints department from 2010.