When Flurry of Blades kills a unit during a resolving chain, does Immortal Phoenix's triggered ability immediately trigger and add itself to the resolving chain, or does it wait until the next Open State?

Ruling: Immortal Phoenix's triggered ability triggers immediately and is added to the chain after Flurry of Blades resolves. It does not wait for the next Open State.

Sequence:

• Flurry of Blades resolves
• Phoenix triggered ability is put on chain
• Any player can react to it
• Phoenix triggered ability starts resolving
• You can pay {1}{F}
• If you paid, Phoenix itself is put on chain as pending item
• Phoenix triggered ability ends resolving
• Phoenix itself starts finalizing
• Make all necessary choices (where to put it)
• Phoenix finalized and resolves immediately (put at chosen location)

Nuances:

• All main deck cards and abilities start as pending items on the chain
• The pending items concept delays making necessary choices and paying costs during resolution of another item
• In most cases the pending concept doesn't need to be explicitly considered, though all chain items technically start as pending