Hello,
The audio files are in the format ending .swf. Your iPhone 6 may not play that file type. The audio files consist of short (5-15 second) clips of the teacher's voice repeating an important point from earlier on the page.
I will look into the problem, and see if there is a solution, however for now please continue with the course, there is no content in the audio files that is not in the text portion of the course.
Sandra King.
Tech Support.