Ottawa also acquired defenceman Cody Donaghey and forwards Matt Frattin, Casey Bailey and Ryan Rupert.
The Maple Leafs get defenceman Jared Cowen and forwards Milan Michalek, Colin Greening and Tobias Lindberg, along with a 2017 second-round draft pick.
Phaneuf, the biggest name in the deal, has 24 points and 67 penalty minutes in 51 games for Toronto this season.
Ottawa starts the day four points out of a playoff spot in the Eastern Conference after a 5-1 win over Tampa Bay last night. Toronto, which lost 6-1 to Ottawa on the weekend, is second-last in the conference standings.