The phrase "primary medium" refers to the main way or tool that is used to convey or communicate a message or information. It is the most important or commonly used method or channel. Full definition
There are many great artists whose primary medium include pencil and paper, but the artist's sketch is not always intended as a finished work. (hifructose.com)
To present your intellectual thoughts to an academic audience, essays are considered as the best primary medium. (studentsassignmenthelp.com)
Her present day primary mediums are natural fibers and clay. (artleagueli.net)