28-year-old Phillip Blanks -- who played at Saddleback College in Mission Viejo, CA -- was at his home in Phoenix when he saw a nearby apartment was ablaze.

Blanks decided to check out the scene to see if he could help ... and noticed a 30-year-old mother preparing to throw her child off the balcony.

Blanks -- who is also a retired U.S. Marine -- immediately knew what he had to do ... and sprinted to the ground below to save the boy from hitting the ground.

"Instinct. There wasn't much thinking. I just reacted. I just did it," Blanks told ABC7.

"The guy who was there with me ... it looked like he wasn't going to catch him. So that's why I stepped in. I just wanted to make a better catch."

Blanks rushed the child to safety ... but the mother tragically passed away from the fire, according to ABC7.

"She's the real hero of the story," Blanks told the outlet. "Because she made the ultimate sacrifice to save her children."

The woman's 3-year-old and 8-year-old were taken to a nearby hospital, where they were treated for non-life threatening injuries.

BTW -- according to Blanks' college bio, he's related to Barry Sanders and Mike Conley.