The 117-103 defeat was the Nuggets' third in their last four games.
The head coach told reporters: "Once again our defense failed us.
"We gave up 117 points for the fourth consecutive game and it happened from the starters through the guys who came off the bench.
"The guys who came off the bench [for Phoenix] played so well they never had to come back to their starters."
The Nuggets sit third in the Northwest Division with a 20-20 record.