Figured out the answer
Inside the phone and behind the display is a V-shaped metal spring which engages with a plastic arm attached to the rear of the display.
When pulling up the display we sometime pull hard and it bends the spring closing the V, and prevents it from stopping on each step of the arm.
Take the back cover off the phone, remove the spring piece (one screw removes it) and open the V back up to like a 60 degree angle. Re-attach the spring and try moving the display. If it still wont move up and down open the metal spring V more until the display moves freely up and down and stops at each step of the plastic arm.
Basic ability to use a screw driver and pliers will fix this for you.