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

Grafdigger's Cage states that creature cards can't enter the battlefield from a graveyard, and that players can't cast spells from graveyards or libraries. This second clause directly prevents any creature card from being cast via flashback, since flashback lets you cast a card from your graveyard (CR 702.33a).

Flashback is a static ability that grants an alternative cost and allows casting from the graveyard (CR 702.33b). However, Grafdigger's Cage's restriction is a blanket prohibition on casting spells from the graveyard, which overrides the permission granted by flashback. A permission and a prohibition on the same action means the prohibition wins (CR 101.2).

Note that Grafdigger's Cage affects creature cards specifically for the 'entering from graveyard' clause, but its 'no casting from graveyards' clause applies to all spells — so even a non-creature spell with flashback would be blocked. That said, the question here is specifically about creature cards, and yes, they are doubly blocked: they can't be cast and couldn't enter anyway.

Example: You have a Gravecrawler in your graveyard. Even if Gravecrawler had flashback (hypothetically), Grafdigger's Cage would prevent you from casting it from the graveyard. Attempting to do so simply isn't a legal action while the Cage is on the battlefield.