I haven't heard 'feature phones' since I used to read consumer electronics news sites (like Engadget, then This is my Next/The Verge) years ago.

I don't think anyone else uses the term; to the layman, they're 'dumb phones', to contrast with 'smart' (although increasinly 'smart phones' are just 'phones').

Or since those are American sites, perhaps it's actually a variation of regional colloquialisms.