Despite being labeled as a planet, Anur Phaetos is technically nowhere near that. Phaetos is an anomaly, caused by the death of a cosmic being. It can be more accurately labeled as a small pocket dimension.
The inside of Anur Phaetos almost looks like that of the insides of a living being, with "flesh" landscapes and large bone structures all around. The area is also in a complete darkness, with almost no light to be seen.