Rubins was one of a number of PHD names linked to the job. Others included business director Jonathan Fowles and media directors Lindsay Weedon and Frances Ralston-Good.
In other moves, Fowles is tipped to take up the role of head of planning while executive planning director Mark Holden moves to head of international operations.
Rubins, who has spent seven years at PHD, fills the managing director role left vacant by Blazey after her promotion to chief executive last month.
Rubins, who will oversee the day-to-day running of the media agency, will report to Blazey alongside Holden and executive strategy director Louise Jones.
His promotion follows in the wake of a number of personnel changes at PHD. Last month, agency co-founder and worldwide chief executive David Pattison decided to leave after 17 years.
Blazey's appointment ended months of speculation about whether a chief executive would be sought after the departure of PHD chairman Tess Alps, who left to become the first chief executive of TV marketing body Thinkbox in April of this year.
Pattison's departure followed the roll-out of PHD as a global network. At the time of his resignation, he said he was talking to PHD parent Omnicom about other possible jobs within the group, but had not ruled out external options.
Rubins joined PHD's strategic joint planning department MSc as managing partner in January 2000. He came from MediaVest, where he had been planning director responsible for the £40m Scottish Courage account.
He had joined MediaVest four years before as associate director.
Blazey joined PHD, which is part of Omnicom Media Group, in 1994 and was appointed managing director in 1999.
PHD declined to comment.