The boy's mother, uncle and more children were inside the home when the uncle saw him in the pool.
Neighbors could hear the panic.
"I just head some screaming, you know," said Robert Price.
Firefighters rushed the child to an area hospital. They say the pool had some type of barricade and they're still trying to determine how the boy was able to gain entry.
"All the proper things were there. This just goes to show that even though those were there, these things happen and they happen fast. That's a lot of stress," said Capt. Aaron Ernsberger of the Phoenix Fire Department.
Neighbors say the family recently moved into the home.
"It's just a tragedy. It is sad," said Ted Lips.
Price added, "It's pretty said.. this stuff happens all the time, you know. It's pretty tough."
In March, there were eight drowning incidents in Maricopa County and we're still a ways away from pool season. Firefighters say nothing can replace the watchful eye of an adult.
"We take it personal.. We want to hope that we're doing the right job. We want to reach out to the public. We want to make the awareness. We're doing everything we can and we are trying to do more," said Ernsberger. "We hurt for the families and really, that's why we go through all these things and try to mitigate these problems."
In addition to those eight drowning calls in March, PFD says there have been a total of 19 incidents in 2015. Friday's fatality marks the second so far this year.