Runeblade Anvil

For Runeblade Anvil, your "next Ending Phase" is whichever of your Ending Phases begins first after its triggered ability resolves. The ability creates the play permission when it executes.^407.5 That permission remains active only for the time stated by the effect.^391.4392

• Earlier in your turn: If the ability resolves before that turn's Ending Phase begins, that same Ending Phase is next.^316.9.b The permission ends when the game enters that phase.
• During your Ending Phase or another player's turn: If the ability resolves during your Ending Phase, that phase has already begun. If it resolves during another player's turn, that turn's Ending Phase isn't yours. In either case, your next Ending Phase begins on your following turn.^115.1.c317.3 The permission ends when that phase begins.