Jason Josaphat, 19, called his mother as a gunman opened fire to ask for help, his aunt and uncle said.
She stayed on the line with him and could hear gunshots in the background, but tried to calm him down as he hid in the bathroom, Jimmy and Myrleine Inelus told KPNX-TV in Arizona, where Josaphat went to high school.
His mother then didn't hear anything for as many as 20 seconds.
"It was dead silence on the phone ... I think that's when the gunman finally made his way into the bathroom," Jimmy Inelus said.
Josaphat moved to Orlando after graduating from high school in 2014. A childhood friend, Messiah McMillian, told KNXV-TV in Phoenix that he was one of the first people whom Josaphat told he was gay.
"When I found out, I never judged him," McMillian said. "I never looked at him any differently. He was always my friend."