Since you're going on week 2, I would think that it may not be related to teething. From what I have heard, and from my limited experience with my two babies, teething troubles only last for a couple of days at a time. As for it being a phase, I don't know. It could be. Again, in my limited experience, "phases" with babies don't usually last so long (phases last longer as they get older:).
My firstborn also loved his formula then he suddenly refused it, but he was 11 1/2 months old at the time, so we just went to milk. But at 9 months, he still really needs all of the nutrients from formula or breastmilk, so I would talk to his pediatrician right away to figure out how you can supplement with other foods. Maybe try a different formula? I know that is an expensive experiment, but it might work. Otherwise, keep offering him lots of water and watered-down juice, and find out how to supplement with the other nutrients he needs. Iron is easy enough to supplement with food (oatmeal and raisins are a great source and my babies loved that from early on) but I don't know where he can get the DHA/RHA and if there are other critical nutrients he needs from formula.
I'm sure he will be fine, this is just one of the many puzzles we have to learn to solve as parents. But there is a solution and I'm sure you will find it. I wish you the best!