If you can access it, point your phone at them. If you can actually get it recording, do so, and try to get the license plate in the video.
In this case, video is better so you can submit it to the authorities and report the harrassment.
Don't expect immediate relief, if any, although some precincts will actually send a letter/warning. However, if anything ever happens in the future, to you, or another cyclist, this will be another piece of evidence against them. The video is what got that driver in TX convicted.