I don't think it was ever common, since earphones weren't that popular until people started calling them "earbuds", but the term was historically used in at least some circles in the U.S. The 1988 Radio Shack catalog [1] seems to mention "earphone" 57 times, including two mono earphone products.
[1] https://www.worldradiohistory.com/Archive-Catalogs/Radio-Sha...