Phoenix
The Phoenix is a creature from Greco-Roman mythology, a fiery bird with metaphysical connections to the sun said to live in Arabia. Its most famous trait is its immortality, which it achieves by ceremonially immolating itself when it grows old and feeble, only to be reincarnated as a chick from the ashes.
In fantasy gaming, as popularized by Dungeons & Dragons, Phoenixes tend to be a species rather than a single individual. Like the Unicorn, they have been generally associated with the Good branch of alignment, mostly because of their adoption as a Christ-figure in Christianity and their long association with healing, life, renewal and immortality in general. They tend to be significantly more badass, often given both elemental control over fire and/or allowed to resurrect themselves in combat.
In WH40K
In WH40K however, the Phoenix is a super-heavy aircraft in the Eldar army. Unlike most Eldar aircraft, the Phoenix sacrifice speed and maneuverability in order to carry FUCKHUGE weapons payload for ground attack missions. The Phoenix along with its smaller cousin the Nightwings work in symbiosis; with the Nightwings clearing the skies of enemy aircraft and escorting Phoenixes as they rain destruction upon ground forces. However despite lower top speeds, the Phoenix is still a thousand more times faster than their Imperium counterparts, what with most Eldar aircraft looking sleek and aerodynamic while some Imperial aircraft looks like they are massacring the air with their fleet of flying cargo containers.
In terms of armaments and the amount of Dakka it can carry, the Phoenix holds a pair of twin-linked Shuriken Cannons mounted in the craft's nose for engaging other aircraft or infantry units, while below the fuselage is a single centerline-mounted Pulse Laser for pinpoint accuracy against hardened ground targets such as Terminators or Dreadnoughts. The Pheonix's main ground attack weapons are twin Phoenix Missile Launchers which can also be mounted in the fuselage or in wing mounts. They typically carry plasma missiles for saturation bombardment of a target, but may replace it with a complement of Krak Missiles. Alternatively, some Phoenix bombers will instead carry the same deadly Monofilament Weaponry as found on the ground-based Night Spinner in place of missile launchers.
It also comes equipped with the usual Holo-fields to make it hard for the enemy to shoot down.
Void Dragon Phoenix
The Void Dragon Phoenix is a variant of the Eldar Phoenix fighter-bomber, flown by an Eldar Corsair warband known as the Void Dragons (Not to be confused with the actual Void Dragon). The only difference between this variant and the original is the replacement of the fuselage Pulse Laser with twin-linked Starcannons. As the Void Dragons have sold their services to both the Craftworld Eldar and Dark Eldar, so too has the Void Dragon Phoenix flown in support of both brethren.