The "Three Billboards Outside Ebbing, Missouri" star got emotional when asked about his speech backstage.
Rockwell explained that Hoffman was "an old friend" who once directed him in a play at the Public Theater in New York City.
"He was a great inspiration and a great theater director," Rockwell said, adding that they were "very close."
"He inspired me and I could go on for an hour about Phil Hoffman," he continued. "Philip Seymour Hoffman was a good friend and he was a huge, huge inspiration on me."
Hoffman, who won a best actor Oscar in 2006 for his role in "Capote," died of acute mixed drug intoxication in 2014 at the age of 46.
"Three Billboards Outside Ebbing, Missouri" was nominated for seven awards, including best picture.