Phasing is a keyword ability.
It represents the removal from existence caused by Teferi's experiments. A permanent with phasing enters and leaves play without any involvement by the player. At the beginning of a player's turn, during the untap step but before untapping; any permanents with phasing in play phase out and any phased out permanents phase in.
When a permanent is phased out, it is treated as if it doesn't exist. It cannot be affected by the game in any way (except effects referring specifically to phased out permanents such as Time and Tide). Being phased in or out is a status, like tapped or flipped, which is only relevant for permanents (objects on the battlefield); a permanent that phases out doesn't leave the battlefield, so it doesn't trigger any leaves-the-battlefield abilities; and a phased out permanent is still on the battlefield, so when it phases in again i t doesn't change zones and it doesn't trigger any enters-the-battlefield abilities. It retains the status it previously had (tapped, flipped, etc.) and any counters, enchantments or equipment on / attached to it will phase out and phase in along with it, still attached.
Phasing out is unrelated to exiling. A permanent that phases out remains on the battlefield (unless it's a token, in which case it ceases to exist); it doesn't go to the exile zone. Only permanents (i.e. objects on the battlefield) have status; even if a card in your graveyard or in exile has phasing, it's neither phased in nor out, so it doesn't phase in and come back into play during your untap step.
Formerly, phasing triggered "leave play" events but not "enter play" events. It was this point and many others that caused players confusion over phasing and prompted a similar ability with simpler rules, flickering, to replace phasing in future blocks. As of the rules updates in October 2005, phasing no longer triggered "leave play" events.
- 702.25a Phasing is a static ability that modifies the rules of the untap step. During each player’s untap step, before the active player untaps his or her permanents, all phased-in permanents with phasing that player controls “phase out.” Simultaneously, all phased-out permanents that had phased out under that player’s control “phase in.”
- 702.25b If a permanent phases out, its status changes to “phased out.” Except for rules and effects that specifically mention phased-out permanents, a phased-out permanent is treated as though it does not exist. It can’t affect or be affected by anything else in the game. A permanent that phases out is removed from combat. (See rule 506.4.)
- Example: You control three creatures, one of which is phased out. You cast a spell that says “Draw a card for each creature you control.” You draw two cards.
- Example: You control a phased-out creature. You cast a spell that says “Destroy all creatures.” The phased-out creature is not destroyed.
- 702.25c If a permanent phases in, its status changes to “phased in.” The game once again treats it as though it exists.
- 702.25d The phasing event doesn’t actually cause a permanent to change zones or control, even though it’s treated as though it’s not on the battlefield and not under its controller’s control while it’s phased out. Zone-change triggers don’t trigger when a permanent phases in or out. Counters remain on a permanent while it’s phased out. Effects that check a phased-in permanent’s history won’t treat the phasing event as having caused the permanent to leave or enter the battlefield or its controller’s control.
- 702.25e Continuous effects that affect a phased-out permanent may expire while that permanent is phased out. If so, they will no longer affect that permanent once it’s phased in. In particular, effects with “for as long as” durations that track that permanent (see rule 611.2b) end when that permanent phases out because they can no longer see it.
- 702.25f When a permanent phases out, any Auras, Equipment, or Fortifications attached to that permanent phase out at the same time. This alternate way of phasing out is known as phasing out “indirectly.” An Aura, Equipment, or Fortification that phased out indirectly won’t phase in by itself, but instead phases in along with the permanent it’s attached to.
- 702.25g If an object would simultaneously phase out directly and indirectly, it just phases out indirectly.
- 702.25h An Aura, Equipment, or Fortification that phased out directly will phase in attached to the object or player it was attached to when it phased out, if that object is still in the same zone or that player is still in the game. If not, that Aura, Equipment, or Fortification phases in unattached. State-based actions apply as appropriate. (See rules 704.5n and 704.5p.)
- 702.25i Abilities that trigger when a permanent becomes attached or unattached from an object or player don’t trigger when that permanent phases in or out.
- 702.25j Phased-out permanents owned by a player who leaves the game also leave the game. This doesn’t trigger zone-change triggers. See rule 800.4.
- 702.25k Phased-out tokens cease to exist as a state-based action. See rule 704.5d.
- 702.25m If an effect causes a player to skip his or her untap step, the phasing event simply doesn’t occur that turn.
- 702.25n Multiple instances of phasing on the same permanent are redundant.