I think there was a story about this not too long ago, where they were showing Phobos's shadow being cast on Mar's surface.
Oklahoma on the night of August 14, 2001 and again on August 19, 2001 to observe Mars himself in the 24-inch f/16 Cassegrain telescope. On both nights, neither moon was observed, while fainter stars were observed. If only Phobos were missing and Deimos were present, one might argue that Phobos is a difficult target, and that either the author or his telescope was just not up to the task. However, the author has a personal friend who observed Deimos a few years ago in a 17-inch Dobsonian telescope (but at a higher altitude in the sky). One might also argue that Mars is low in the sky, but the faint stars he observed were just as low.
I was also wrong about Deimos when I published Phobos and Deimos Have Vanished. I sincerely regret that mistake, and I apologize to all of my readers for having made it. Ironically, when I published that mistaken article on August 21, 2000, I had already looked at the photograph that I had taken two days earlier that contained the image of Deimos, but I did not see it at that time. It was not until weeks later that I looked at the same photograph again, and I saw it.