HiRISE on Phobos: Building-Sized Boulder or Possible Monolith?

To the point

HiRISE images show a bright, rectangular feature on Phobos that could be a five-meter bedrock fragment casting a shadow, sparking monolith speculation by Buzz Aldrin while Yisrael Spinoza cautions it is likely natural, with Efrain Palermo and Lan Fleming analyzing it as a physical anomaly and Scott Waring later claiming a larger alien monolith, alongside historical remarks by S. Fred Singer, Carl Sagan, and Shklovskii about the possibility of artificial structures.