Well, Personally I haven't done a lot of work in that area, But I do know it has phasing issues. Most likely the phasing spell was initiated by the quest or a condition statement in the database. When it should have been handled by the spell_area table. This way you can say, If your still on certain quests, Then cast that phasing spell, But only in that area. Sort of a combination of using spell_area, And a conditions statement to achieve that result.
If someone would like to read the quest, and search for any existing spell_area rows containing that area id. Or conditions for that quest. You can learn a lot about phasing real quick. And if your unable to make sense of it all. Just post what you have found on this post, And we can all figure it out together. Because obviously it isn't setup correctly right now.
Keep in mind, That you need to play through the area, So that you can make your best guess as to when the phasing should change, This will tell us when it should be removed in the condition statement.