The M'Kraan Crystal is the doorway to the nexus of all realites (past, present and future) in Marvel.  The nexus is in fact the White Hot Room, also known as the center of creation and the heart of the Phoenix.  The White Hot Room is a realm made of pure energy (the Phoenix in it's native state) and borders all realms from the material to the imaginary.  It is from this realm that the various hosts and the avatar of the Phoenix do their Phoenix work, while they wait to resurrect.  Entire universes can be absorbed into this plane and healed or destroyed without even a hint of paradox.  The White Hot Room also serves as a waystation that all beings pass through at one point in time before their birth or after their death until they reach their destination either in life or the realm of Death; in essence "You are always there waiting for yourself to arrive."