I hear that after you deliver the broken phial to Nurelion, you get a letter from Quintus about repairing it - but I turned it in long ago, weeks ingame, and still no letter. Does it usually take more than a few days or is it just not triggering for some reason?

You need to progress far enough in the main quest to be able to access the Throat of the World.

I just got that letter yesterday after delivering the Phial months ago (real life time).

Or do what the guy above me said, and reach the throat of the world.

Ahhhh, okay, that explains it! Thanks.