Jason Peters was absent from Tuesday's organized team activity and hasn't attended the voluntary workouts since the first OTAs were held from May 13 to 15.

OTAs are voluntary, but Eagles coach Chip Kelly said that he knew of Peters' whereabouts and that his absence wasn't injury-related. The all-pro left tackle is returning from a ruptured Achilles tendon that caused him to miss last season.

"We know where he is, and we know what's going on," Kelly said.

Asked whether Peters would be in attendance for the rest of this week's OTAs or for next week's mandatory three-day minicamp, Kelly said, "I expect him here shortly."

Attempts to reach Peters through his agent, Eugene Parker, were unsuccessful.

Kelly, for the most part, had full attendance during the first two weeks of workouts. The Eagles said that Peters, along with several other players, missed last Monday's practice because of travel delays. Kelly, though, said that Peters missed all of last week.

Peters had been participating in all facets of practice. Eagles offensive line coach Jeff Stoutland told reporters last week that he thought the 31-year-old Peters was practicing as if he had never had his injury.

With Peters missing, Dennis Kelly slid over to left tackle, and rookie Lane Johnson moved up to the first team at right tackle. The Eagles' top pick had been working exclusively with the second team up until Tuesday.

"I went with the 'ones' today, and I had to help out with the 'threes' sometime," Johnson said. "It wasn't too bad."

Expected starting left guard Evan Mathis (ankle) and center Jason Kelce (knee) continued to be eased back from surgeries. Mathis participated in some conditioning drills for the first time since his ankle was cleaned out three weeks ago. He isn't slated to fully practice until training camp in late July.

Kelce, who is still being held out of 7-on-7 and team drills, said that he is slated to be "full go" the day before camp begins.

With Mathis out, Danny Watkins took the first team repetitions at left guard during two open practices over the last two weeks, but veteran Allen Barbre took his spot on Tuesday. Barbre, signed as a free agent this offseason, spent part of last season with the Seattle Seahawks.

Dallas Reynolds was once again at center in place of Kelce. Right guard Todd Herremans was the only penciled-in starter that practiced with the first team.

Phillips sits out

Kenny Phillips, who has a long history of knee injuries, missed Tuesday's wet practice for what he said were precautionary reasons.

The Eagles safety said that he was taking it easy on his left knee, per a team spokesman. Phillips had microfracture surgery on the knee in 2009 and missed most of that season. An MCL sprain in his right knee sidelined the former New York Giant for nine games last season.

Kelly would only confirm that Phillips missed practice - held in a steady rain - because of his knees. He also said that his absence had "nothing to do with the weather."

But was it a setback?

"I don't ask questions," Kelly said. "They just tell me who's going and who's not going."

Phillips was signed as a free agent this offseason at relatively low cost. Virtually none of his salary is guaranteed. The Eagles were taking little risk on a player who has missed a number of games in his career because of knee issues.

Originally asked if Phillips had an injury, Kelly quipped, "Yeah, he's had an injury for a couple of years now."

Phillips had been running with the second team along with Kurt Coleman. David Sims and rookie Earl Wolff took Phillips' reps. Nate Allen and Patrick Chung continued to be the first team safeties.

Extra points

Tight end James Casey, who underwent arthroscopic knee surgery last week, stood and watched practice. "He's not going to go during OTAs or minicamp next week," Kelly said. "But we anticipate full recovery and to be ready by training camp." . . . Linebacker Chris McCoy (knee) was a partial participant.

Contact Jeff McLane at jmclane@phillynews.com. Follow on Twitter @Jeff_McLane.