Does Noxian Guillotine's delayed trigger count as killing a unit with a spell for Immortal Phoenix?

Ruling: Yes, Noxian Guillotine's delayed trigger counts as killing a unit with a spell and will trigger Immortal Phoenix.

Nuances:

• The retired FAQ suggested delayed kills don't count, but this FAQ has been officially retired
• The Core Rules state that abilities originating from game objects (like delayed triggers) are responsible for kills in addition to the game object that created them
• Imperial Decree works the same way as Noxian Guillotine for this interaction