Phillips, who had two interceptions in Sunday night's win over Dallas, was placed on injured reserve by the Giants (2-0) on Thursday because of an unhealthy left knee. The team also announced it was awarded safety Aaron Rouse off waivers from Green Bay.
"I really feel for Kenny because he had worked so hard during the offseason to prepare himself for the '09 season," general manager Jerry Reese said. "He had a great camp and was just beginning to come into his own and showed flashes of being one of the premier safeties in the NFL. We expect him to recover from this setback and come back stronger than ever. This league is about making adjustments and we will do that."
Phillips had been bothered by the knee since training camp. An MRI on Wednesday revealed that the patella femoral arthritis in his knee has worsened. A final determination has not yet been made on how to treat the condition.
Phillips was stunned that he would have to miss the rest of the season.
"It never crossed my mind, ever," Phillips said. "I knew the situation. I just felt I could push it through the season. So to get this news is a real shock."
Phillips was leading the team in interceptions (2) and tackles (16) and was tied for the lead in passes defended (2).
"The most important thing for us right now is to realize it's an emotional time for Kenny Phillips," said coach Tom Coughlin, noting that Phillips looked like he had lost his best friend after getting the news. "He had an excellent training camp. He played the deep ball, really, unlike anybody we've had around here."
With Phillips out, C.C. Brown will start Sunday at Tampa Bay.
The 31st overall selection in the 2008 draft, Phillips played in every game and had three starts as a rookie. He finished with 66 tackles (43 solo), seven passes defended and an interception.
"That is probably the toughest part. I worked hard this offseason and I felt like this was going to be a big year not only for me, but for the Giants," Phillips said. "I started the season off pretty well with a few tackles, interceptions and for it to just get snatched away from me like this is real tough."
Phillips, who missed two of the Giants' four preseason game, does not know when he hurt his knee.
"Everybody gets nicks and bruises in training camp, so that's just what I thought it was," he said. "Swelling occurred, but most people get swelling. As long as it goes down, it's not a big deal.
Phillips is the third Giants player to go on injured reserve. Rookie running back Andre Brown ruptured his Achilles' tendon in training camp. Defensive tackle Jay Alford suffered a knee injury in a preseason game in Chicago.
Rouse, 6-4 and 227 pounds, had nine tackles in Green Bay's 31-24 loss to Cincinnati last week. He had three solo tackles in the season-opening victory over Chicago.
A third-year pro, he has played in 27 games with 11 starts. He has 113 tackles (80 solo), seven passes defended and four interceptions, including a pick of Peyton Manning that he returned 99 yards for a touchdown last Oct. 19. It was the longest interception return in Lambeau Field history.
Injuries in the secondary have become a concern for the Giants. Cornerbacks Aaron Ross and Kevin Dockery missed the opening two games with hamstring injuries and don't appear ready to play this weekend.