Austenite is a high temperature phase and has a Face Centred Cubic (FCC) structure [which is a close packed structure]. The alpha phase is called ferrite.

Does austenite have two phases?

Austenitization, which means heating iron or an iron alloy, such as steel, to a temperature at which its crystal structure transitions from ferrite to austenite. Two-phase austenitization, which occurs when undissolved carbides remain following the austenitization step.

Is martensite a phase?

Following the definition, martensite is simply a phase. Now when the as quenched martensite is subjected to tempering (in steels), the carbon supersaturation is released resulting in the decrease of tetragonality, recovery, etc.