The Heat were without Dwyane Wade because of a foot sprain.
James tweeted overnight that he'd caught a bug that has been going through the Heat during their six-game road trip the last week.
He posted a picture of himself wrapped up and said he had a headache and a stomachache. Wade missed a game last Sunday because of sickness. James, who also suffered a bruised shoulder Thursday in Denver, was not at the team's morning shootaround in Phoenix.
Wade also skipped the workout and missed his second straight game with a left foot injury. The Heat's next game isn't until Wednesday against the Milwaukee Bucks in Miami.
Giving Wade the next game off would give him a full week to recover.