Hint 1
You need to charge the crystal with lasers. For that you'll need to enter the laser control room in the auditorium.
Hint 2
Have an inventory item open already when you click on the door. Do you have something that can create sound?
Hint 3
You have to play the right sequence of notes on the phone to open it. The laser technician must keep the correct tune handy so she can easily go into the laser control room.
Hint 4
Play her ringtone to open the door. If you're still stuck, you can check out my reply to the comment below this one.
