[Update 8:59 p.m.] A Southwest Airlines flight made an emergency landing at Phoenix Sky Harbor International Airport Monday afternoon. 

Southwest Airlines Flight 2675 made an emergency landing Monday due to a "possible threat," reports KNXV-TV. The plane was traveling from Los Angeles to Austin, Texas. 
The specifics of the threat are still unknown, but Southwest spokeswoman Katie McDonalds said the pilot learned of a "security concern" and requested to land at the Phoenix airport. 
The plane was carrying 143 passengers and is currently separated from any of the airport terminals. Passengers will be boarded back onto the same plane if it is given the clear. If not, they will be placed on another plane to complete their travel schedule. 
Phoenix Sky Harbor spokeswoman Julie Rodriguez says arriving and departing flights have not been affected by the incident. 

According to a statement released by the FBI, the bureau and "law enforcement partners" are currently investigating following a "telephonic bomb threat to an aircraft made this afternoon."
"The flight, destined for Texas, departed LAX at 2:12pm and was diverted to Phoenix for further investigation.
The flight landed safely in Sky Harbor Airport in Phoenix and the aircraft is being directed to an isolated area at the airport," continues the statement.
"The FBI and law enforcement partners are responding to conduct an investigation of the aircraft, as well as to determine the person/s responsible for the threat."

A North American Aerospace Defense Command spokesperson said two fighter jets from Davis-Monthan Air Force Base watched the diverted plane through air patrol.

Brad Hawkins, a spokesman for Southwest, cofirmed that Southwest Airlines Flight 2675 "landed in Phoenix to look into a possible security threat." He added that all 143 passengers were safely deplaned "via airstairs" and will be placed on new flights to Austin as soon as possible.