He takes over from Kent Ertugrul, who will continue in his role as chief executive. The appointment comes into effect immediately.
Heyer has held a number of high-profile roles at companies including Young & Rubicam, where he was chief operating officer, and Turner Broadcasting System, where he held the same role. He has been on the board of Phorm since October last year.
Ertugrul said: "Splitting the role of chairman and chief executive will enable me to focus more of my time and efforts on driving our vision.
"I am very pleased to be working even more closely with Steve. Steve's broad business experience, commercial acumen and deep knowledge of the media, advertising and ISP industries will continue to prove invaluable to Phorm going forward."
Phorm is behind technology that analysis web users' behaviour in a bid to serve up more relevant advertising.
Phorm has been criticised because of fears that its technology will allow internet companies to spy on users. However, it has taken great pains to explain that privacy is one of its major concerns and that the way its targeting works, no identifying information is retained on web users.
Heyer joined Coca-Cola in 2001 to head a new ventures unit, where he was charged with developing new products and marketing juices, coffees and teas. He was promoted to the chief operating role in late 2002, but left in 2004 and became the CEO of Starwood Hotels and Resorts.
Before joining Coca-Cola, Heyer was president and chief operating officer of Time Warner's Turner Broadcasting Systems, where he launched 14 new television networks.