11:44 AM PT -- According to the Laundries' family attorney, Steven Bertolino ... they did purchase a new phone, and he believes it's the one Brian left behind at home and the FBI is already in possession of it.
The feds are on the hunt for a burner phone Brian Laundrie allegedly purchased the day he went missing ... TMZ has learned.
Sources connected to the manhunt for Laundrie tell TMZ ... FBI agents recently visited an AT&T store in North Port, FL -- where Laundrie's parents live -- and seized surveillance footage.
We're told Brian allegedly went to the store September 14 with an older woman and purchased the phone before they left.
The timing is significant because Sept. 14 is the date Laundrie's parents claim they last saw him leaving their home. They say he had his backpack and was going to a nearby nature reserve, but never returned. They reported him missing Sept. 17.
We reached out to the North Port AT&T store, where an employee told us she could not confirm or deny Brian was there Sept. 14 and said she was told not to discuss the matter. We also reached out to AT&T corporate, and they told us, "Thanks for contacting us. I have to refer you to law enforcement on this one."
We've reached out to law enforcement ... again, they would not confirm or deny.