Basically the card is referring to the discard phase of the cleanup step.From the Comp. Rulings
3 - Turn Structure
300 - General
301 - Beginning Phase
302 - Untap Step
303 - Upkeep Step
304 - Draw Step
305 - Main Phase
306 - Combat Phase
307 - Beginning of Combat Step
308 - Declare Attackers Step
309 - Declare Blockers Step
310 - Combat Damage Step
311 - End of Combat Step
312 - End Phase
313 - End of Turn Step
314 - Cleanup Step
314 - Cleanup Step
314.1 - If the active player's hand contains more cards than his or her
maximum hand size (normally seven), he or she discards enough cards to
reduce the hand size to that number (this game action doesn't use the
stack). CompRules 2003/07/01]
314.2 - Simultaneously, all damage is removed from permanents and all "until
end of turn" and "this turn" effects end (this game action doesn't use the
stack). CompRules 2003/07/01]
314.3 - If the conditions for any state-based effects exist or if any
triggered abilities are waiting to be put onto the stack, the active
player gets priority and players may play spells and abilities. Once the
stack is empty and both players pass, another cleanup step begins.
Otherwise, no player receives priority and the step ends.
CompRules 2003/07/01]
Comp. Card Rulings
Necropotence:
Info: Color=Black Type=Enchantment Cost=BBB IA(R)/5(R)
Text(5th+errata): Skip your draw step. ; If you would discard a card from
your hand, remove that card from the game instead. ; Pay 1 life: Remove
the top card of your library from the game face down. At the end of your
turn, put that card into your hand. [Oracle 2001/03/07]
Replaces all discards with removing the card from the game. The action is
no longer a discard and abilities triggering on a discard will not
trigger. [D'Angelo 2000/03/03]
Removing Necropotence from play will not stop the cards from the
life-payment ability from being put into your hand at the end of turn.
[D'Angelo 1998/11/13]
Only has the effect of making you skip your draw step if it is in play when
your draw step would normally start. [WotC Rules Team 1995/10/18]
The acquired cards are not considered draws. They will not cause damage
with Underworld Dreams or have Enduring Renewal detect creatures.
[D'Angelo 1995/12/08]
Can be used with Fasting. The reason is that Necropotence does not force
you to skip your draw step unless it is in play at the end of your upkeep
phase. Fasting allows you to mark the draw step as "skipped" during
upkeep prior to Necropotence kicking in. [Aahz 1996/01/16]
Necropotence interacts with Madness (see Rule 502.24) so you cannot use the
Madness ability. This is because Madness turns "discard to graveyard"
into "discard to removed from game" and Necropotence turns any discard
into simply "remove from game" with no discard. Madness only works if
you remove it from game as part of its ability. [Jordan 2002/03/03]
Type 1 tournaments (see Rule 801) have restricted this card since
2000/10/01.
Type 1.5 tournaments (see Rule 802) have banned this card since 2000/10/01.
Extended tournaments (see Rule 803) have banned this card since 2001/04/01.
Note - Also see Skipping a Phase, Rule 419.6e.