"We don't know the details surrounding his death," Mack said. "We don't even know exactly where he was at for sure."
Mack said she learned of her son's death when two Marines showed up at her door at 2 a.m. Saturday. Mack and her husband, Jeff Mack, formerly of Craig, live in Riverton, Wyo.
''I don't think anything can prepare you for two young men standing in the living room telling you your son has been killed,'' Mack said. ''It's just surreal. They were crying.''
She last talked to her son last Wednesday night.
''He said, 'Mom, I'm fine.' He sounded great,'' she said. ''It was really good to be able to talk to him. It made us feel better.''
Mack said she took comfort in the fact that her son died doing what he loved being a Marine. His decision to serve came after a political awakening in high school, she said.
"He was very politically aware," Mack said. "The night of the presidential election, he stayed up all night waiting for the results. He was pulling for Bush.
"After 9/11 it became a compelling force in his life," Mack said. "He felt like he had to do this for his country and his president."
Joining the military isn't anything new for the family. Phelps' father, John Phelps, is a Vietnam veteran. Chance Phelps' sister, Kelley, 22, is a Navy petty officer second class who works at the Pentagon and is engaged to an Army sergeant.
Mack said her son had a gift for making people smile.
"He was a character ... a comedian. He was hilarious to be around and I'm not just saying that because I'm his mom. Chance was always being a cut-up."
Moffat County High School football coach Kip Hafey agreed.
"I don't think I ever saw him without a smile on his face," Hafey said. "He was just a good kid who wanted to help people. On the football team, he was all about doing whatever he could to help the team."
In addition to sports, the young man also loved to hunt and fish and spent summers with his father in Dubois.
Phelps was deployed to Iraq just over a month ago with the 3rd Battalion, 11th Marine Regiment, 1st Marine Division. He was a machine gunner in a humvee, John Phelps said.
Phelps enlisted in the Marines during his senior year at Palisade High School, where he transferred from Moffat County High School.
"He was doing what he wanted to be doing for the first four years out of high school," John Phelps said. "He had other plans he wanted to follow later in life.
"He really wanted to be a father. He always loved little kids and dogs. He was a great big strapping Marine who just loved people."
Hafey said he hopes Moffat County High School students will remember the sacrifice Phelps and others have made in service to their country.
"I would just hope that some of the kids appreciate what it means," he said. "Chance was out there for us."
Funeral services will begin at 2 p.m. Saturday at the Dubois High School gymnasium in Dubois, Wyo. After the funeral, there will be a graveside service, followed by a reception at the high school and a celebration of his life at the Veterans of Foreign Wars post in Dubois.
The Marine Corps will provide a full complete detachment of Marines with an honor guard for the service, Mack said. Pallbearers include Phelps best friend, Pfc. John Hakes Jr. -- they joined the Marines together -- his sister's fiance, Army Sgt. Robert Orndoff, and his recuriter, Staff Sgt. Charles White.
Phelps' grandparents are John and Tonee Gingrich and Tim and InaFaye Mack, all of Craig.
The Associated Press contributed to this story.