iPhone 6 won't play sound through JUST my Bose headphones

I've got this pair of Bose QC25 headphones that I want to use with my iPhone 6. Problem is, when I plug it in the sound comes through the phone's speakers like as if it weren't plugged in. They've worked before; I don't know what happened to change it but they just don't anymore. The Bose headphones work fine on my Macbook, and I also have a set of apple earbuds that work fine with both my phone and my macbook. This isn't a huge deal, it's just kind of weird and I'd like to be able to use my headphones for both.