Green-Beckham, who transferred from Missouri in April 2014 after several run-ins with the law, never played a down for the Sooners. He was not allowed to play this season after the NCAA denied the school's request for a waiver that would have made him eligible to play immediately.
"I knew that was something that could happen," Stoops said Tuesday. "He had great character through here, did well in classes, worked hard for us.
"I believe in young people and helping them improve and move forward in a positive direction. Dorial contributed to us in a positive way."
One of college football's most explosive receivers in 2013, Green-Beckham had a breakout season for the Tigers with 59 receptions for 883 yards and 12 touchdowns as a sophomore. He was one of the nation's top recruits in the Class of 2012, ranking No. 3 in the ESPN150.
ESPN NFL Draft Insider Mel Kiper Jr. rates Green-Beckham as his fifth-highest receiver in his draft positional rankings, but believes that a full season at Oklahoma was best for him to transition to the NFL effectively. Scouts Inc. rates him 10th at receiver.
His admission to Oklahoma came with specific stipulations, including continued rehabilitation and drug testing, according to a source. Green-Beckham also was subject to a zero-tolerance policy that included any failed drug test.
The 6-foot-6 receiver was kicked out of Missouri's program after an initial suspension. His troubles included being investigated for allegedly pushing an 18-year-old female Missouri student down at least four stairs. No charges were filed, and the case was closed after the student and a roommate declined to press charges.
Green-Beckham also had two marijuana-related arrests during his time at Missouri.
Phillips, a 6-6, 334-pounder, had 38 tackles, including seven for losses, this season. Kiper also has Phillips rated fifth among defensive tackles in his position rankings.
Jake Trotter of ESPN.com and The Associated Press contributed to this report.