The Suns are 28-23 so far this season.
The coaching change could take place Monday, the newspaper said.
Gentry -- a former head coach of the Miami Heat, Detroit Pistons and Los Angeles Clippers -- has been an assistant on the Suns coaching staff since 2004.
Porter, who formerly coached the Milwaukee Bucks and was an assistant under Flip Saunders in Detroit, became the Suns' coach in June 2008.
Swim Week Miami Beach 2014 [PHOTOS]