Stephen Heyer, the non-executive chairman, only joined the company in August.
Phorm announced the departures in a statement carrying no comment from any of the four men, who include chief operating officer Virasb Vahidi and non-executives David Dorman and Christopher Lawrence.
Phorm has replaced the three non-executives with former chancellor of the exchequer Norman Lamont, former Ofcom chief policy partner Kip Meek and investment banker Stefan Allesch-Taylor.
In the statement Kent Ertugul, chief executive of Phorm, thanked the four men for their "important contributions" and welcomed the new arrivals: "They bring extensive experience on government, business, regulatory matters and financial markets.
"As we move into the next phase of our development, the priority will be to build momentum in the rollout of our strategy."
Phorm has been hit by hold-ups in its attempt to roll out its behavioural tracking system Open Internet Exchange to ISP customers such as BT because of concerns over its impact on users' privacy.
Privacy campaigners took exception to BT trialling the system in 2006 and 2007 without asking its users for their consent. According to IT news website The Register one campaigner is attempting to bring a private prosecution.
Phorm received a boost in September when the Department for Business, Enterprise and Regulatory Reform declared its technology was legal.