Does Grafdigger's Cage prevent cards from being cast from the graveyard using flashback?

Grafdigger's Cage states that player's can't cast spells from graveyards. Flashback is a keyword ability that allows a player to cast a card from their graveyard by paying the flashback cost instead of the mana cost (CR 702.33a). Because the spell is still being cast from the graveyard, it falls squarely within what Grafdigger's Cage prohibits.

The key distinction is between casting and other ways of putting cards onto the battlefield. Grafdigger's Cage specifically targets the act of casting from a graveyard. Flashback does not change where the card is being cast from — the card remains in the graveyard until it resolves or is exiled, and the casting itself originates from the graveyard zone (CR 601.2, 702.33b).

This means that as long as Grafdigger's Cage is on the battlefield, a player cannot use flashback on any card in their graveyard. The cage effectively shuts down flashback entirely for all players.

Example: Your opponent has Grapeshot with flashback in their graveyard. You control Grafdigger's Cage. Your opponent cannot pay the flashback cost to cast Grapeshot from their graveyard — the Cage's replacement effect prevents the cast action from being taken in the first place.

Note that Grafdigger's Cage does NOT prevent cards from being exiled via flashback's exile-instead-of-graveyard replacement effect if somehow the spell were cast; but since the cast itself is illegal, the entire flashback action is blocked (CR 702.33c).