Is there a regulation or order that prohibits Marines from reading something on their cell phone while walking in uniform?

The closest thing I can find is paragraph 1004.4c below pulled from MCO 1020.34H (May 2018), which only mentions talking on the phone.

"In order to maintain good order and proper military courtesies, conversations on cellular phones (to include the use of the earpiece), while walking in uniform, indoors or outdoors, are prohibited. The use of electronic equipment (i.e. portable audio devices) is not authorized while exercising in uniform except as authorized per command/facility regulations."