Phillips has been initially diagnosed by team doctors with an MCL sprain, a team source told ESPN's NFL Insider Adam Schefter.
Phillips said he'll have an MRI on his knee Monday morning, but that his ACL is "good." When asked how long he'll be out, Phillips said, "I don't know."
Phillips suffered the injury when he collided with linebacker Chase Blackburn while trying to tackle Packers tight end Jermichael Finley after Finley made a 23-yard reception with 5:40 remaining in the second quarter. The collision sent Phillips violently to the ground.
He stayed on the ground and was visited by the team's training staff, but eventually got up and walked off gingerly under his own power before heading into the locker room.
The 25-year-old Phillips was forced to undergo microfracture surgery on his knee after suffering a season-ending injury during Week 2 in Dallas back in 2009.
Meanwhile, Giants rookie linebacker Spencer Paysinger was the first to go down with a strained hamstring early in the second quarter and was declared out for the rest of the game.
Packers star cornerback Charles Woodson suffered a concussion. Woodson was hurt in the fourth quarter and did not return to the Packers' 12th straight victory without a loss. He will be examined further back in Green Bay this week.
Backup tight end Andrew Quarless left late in the period with a sprained right knee, needing help to get to the sideline. Coach Mike McCarthy termed it "serious."
Green Bay also lost running back James Starks with a sprained ankle. The team did not reveal which ankle.
Mike Mazzeo is a regular contributor to ESPNNewYork.com. Information from The Associated Press was used in this report.