That came just one day after 7-month-old Zane Endress also died after after being left in a vehicle, the Arizona Republic reports.
Just before 3:00 p.m., Phoenix police officers responded to the area of 2700 E. Marguerite Avenue in reference to an injured child.
"Unfortunately, we hear this, that parents forgot their baby in the vehicle", said Sgt. Mercedes Fortune with the Phoenix Police Department.
FOX10 reports that the baby was under the care of his grandparents at the time of the incident.
According to authorities, the child had been in the vehicle for several hours before he was found.
Police say this is a tragedy that could have been avoided. "Everyone is cooperative", Fortune said.
Phoenix police said there was no evidence of foul play and it appears to be an accident.
Family members began gathering at the church to support the parents shortly after it happened.
"You feel like it's something that could happen to anybody", she said.
She said she had come to the church to support the family, and mentioned hearing about the other baby that had died similarly Friday.
Last year, the organization recorded 29 heatstroke deaths of children left in cars.
Sgt. Mercedes Fortune added "make sure that anybody who enters that auto, for whatever reason, just take the time to actually look and examine the vehicle".
Zettica Mitchell, who told the Arizona Republic she is a cousin of the baby's father, called the death "shocking, devastating, just sad".