The 64-year-old Phillips went on medical leave Dec. 14. He returned last week and worked from the press box in Sunday's 23-22 loss to Tennessee. He'll work from there again when the Texans (10-6) play Cincinnati (9-7) in the playoffs.
"The bottom line is I'm fine, things are progressing well and it's going to take me about six weeks total to get full energy back and be moving around and start lifting and things like that," Phillips said.
Phillips returned to practice last week, though he spent long periods sitting on a golf cart with his father, Bum, the former coach of the Houston Oilers. He says he's been fully involved in preparations for this week's game, though he's felt exhausted by about 5 p.m. each day.
"But it's been getting better," Phillips said. "I've been here this week for all the game planning, which I haven't been previously. All the game plan stuff, all the real necessary stuff, I've been involved in."
Phillips wouldn't offer further details about his condition, other than acknowledging that he had his gall bladder removed. He joked about his medical condition initially, saying he was having a procedure on his kidney.
He explained Thursday that he became ill one day, and team internist James Muntz suggested he undergo further examination.
"Why he did that or whatever, I'm still blessed for that because they found something that needed to get done, and we did it very quickly," Phillips said. "Everything came out well. It was more than we thought it was originally, but it's still done, and everything's positive."
Despite his health issues, Phillips said Thursday that he "should be considered" for head coaching jobs in the future.
Phillips was fired as the Cowboys coach midway through the 2010 season. Houston's defense has made a remarkable turnaround in his first season as coordinator, improving from 30th in 2010 to second overall this year.
Phillips says he's not looking to be a head coach again, though he believes his record (82-59) would make him a viable candidate.
"I don't like to toot my own horn," he said. "I've got a good record. I think I should be considered. I guess people may have taken it the wrong way that I ought to be a head coach. I don't believe that. I think I should be considered. If you look at my record, and you can look at all the people they're talking about now, and my record is better than most everyone they're talking about, as a head coach."
Phillips grew up near the Texas-Louisiana border, played at the University of Houston and worked with under his father with the Oilers in the late 1970s. He's content to stay where he is now, though he'll listen to anyone who'd approach him about a head job.
"If you want a winner, if you want experience, you know, I'd like to talk about it," he said, "but this is the best job I've had. It couldn't be a better job than this, right now and if we keep going the way I think we're going to go, and we're going to be good for a long time, especially defensively I think. So, you know, I'm not looking to go anywhere."
Phillips implemented a 3-4 alignment, and the Texans defense began generating sacks and turnovers from the first game. The players talked all season about the renewed confidence Phillips instilled.
Linebackers coach Reggie Herring called the defense in Phillips' absence. But just having him back has given the team a psychological boost.
"It's very important for him to be out here," said linebacker Brian Cushing, Houston's leading tackler. "It just makes us want to play more for him on top of it."