An immense object can be seen above the clouds in space; it appears to be a Grineer Asteroid base and possibly Mars' other moon Deimos. This is quite remarkable for how large the object is seen in space, perhaps making it the largest Grineer mining operation to date.
Although the Grineer have supposedly occupied the moon recently (one of their most recent occupations anyway) there are signs of very old Grineer equipment scattered and rusting in some places, perhaps suggesting that the Grineer were previously here before but had to evacuate at some point.
The planet is littered with massive wind generators, providing what appears to be the majority of the planet's power, and various pumps and water bays are used to filter and process water.
Due to the level of Iliad, Vor is significantly more powerful on Phobos than he is on Mercury, but Kril is weaker than he is on Ceres.
Sentinels have a very slim chance of surviving during these levels as constant bombardments from Hellions can easily destroy them regardless of how durable they are.
During the cinematic of Captain Vor & Lieutenant Lech Kril on Iliad, some players screens go black, and they wouldn't be able to see what was happening in there.
Kril will often spawn partially inside the large spherical object on the top of the arena area, immobilizing him for the majority of the battle.
Phobos is named after the Greek personification of fear and one of the sons of Ares, who is Mars' Greek equivalent. It has a twin moon called Deimos (strife), the later currently is not available in Warframe and there are no plans on adding it.
In contrast to how Phobos is depicted in-game, in real life it is irregular in shape. It is widely believed to be a captured asteroid.
The nodes on Phobos are named after actual named geological features of Phobos. Other than Monolith and Iliad, those in turn are named either after astronomers (e.g. Asaph Hall, who discovered Phobos) or after characters in Gulliver's Travels (as its author, Jonathan Swift, predicted the existence of Mars' moons).
The boss level, Iliad, is named after an ancient Greek 'epic' poem, which tells of the battles and events during the weeks quarrel between the King Agamemnon and the Warrior Achilles.
This planet was unlocked as a reward for completing the Arid Fear Event. Much of the event involved the Grineer and the Corpus trying to hide Phobos' existence from the Tenno.
Up until The Gradivus Dilemma Phobos was the third planet in the game that was completely under the control of a given faction (besides the indigenous species), following the (then) Infested-controlled planets of Eris and Jupiter.
Phobos is the first planet to have an Assassination mission involving more than one entity. The mission comes up as a "?" but shows a picture of Vor and Kril on the lobby. It is not known why it is marked as "?".
Looking into the distance from the extraction point one will be able to see what looks like a Fomorian ship on its side in the far background.
Phobos' geology appears to resemble Mars in reality, having red soil and a desert like environment.
Phobos is one of the few locations that does not drop Research components.
Captain Vor and Krill as seen in the mission lobby screen
Vor and Kril during the opening cinematic
Vor and Kril together during the fight
Grineer asteroid nase possibly of Deimos, Mars' other moon
Mining station that is mining into Phobos (message says 'Danger', obviously)
Important machine in the center of a cave, seems to be consuming massive amounts of power, what could it be?