Phandalin is a frontier town known for mining and venture capital/venture missions. Unfortunately, even at the town's only market- Barthen's Provisions- there aren't going to be much in the way of musical instruments to be sold there. Mostly supplies and... like the namesake says, provisions. You would, however, most likely be able to find a pan flute or a simple ocarina if that floats your boat! Sorry, Kaede, a true violin will have to wait until you can get back to Fantasy Costco and give a cat some of your good, hard earned cash.