I disagree. I think having device specific stylesheets is a bad idea. Also, with the above structure, if I have phablet.scss open, I’ve no idea which feature it belongs to.
Instead, give your breakpoint variables sensible names and name your stylesheets by feature. Then use media queries with your breakpoint variables to style each feature per device. See how http://refills.bourbon.io/ do this. It makes for very modular code and this is the approach I always recommend, especially with large projects.