Does Grafdigger's Cage prevent creatures from being cast from the graveyard with Flashback?

Grafdigger's Cage states that creature cards in graveyards and libraries can't enter the battlefield, and — critically — that players can't cast spells from graveyards or libraries. Flashback is an alternative cost that lets you cast a card from your graveyard (CR 702.33a), so it falls squarely under what the Cage prohibits.

Because the Cage prevents the casting of spells from the graveyard, a creature card with Flashback simply cannot be cast using that ability while the Cage is on the battlefield. The Flashback ability still exists on the card, but you are not legally allowed to cast it from the graveyard (CR 601.3 — if a player can't take an action, they can't begin performing it).

Note that Flashback on a non-creature spell (e.g., Unburial Rites as a sorcery) is not stopped by Grafdigger's Cage, because the Cage only restricts creature cards from being cast from the graveyard. Only the creature-card restriction applies to non-creature spells.

Concrete example: You have Vengeful Dead (a creature with Flashback) in your graveyard and want to cast it using Flashback. Your opponent has Grafdigger's Cage in play. You cannot cast Vengeful Dead from your graveyard at all — the Cage's restriction on casting creature cards from the graveyard blocks Flashback entirely.

Relevant rules: CR 702.33a (Flashback definition), CR 601.3 (legality of casting), and Grafdigger's Cage's own Oracle text restricting casting creature cards from graveyards.