If a unit dies from Fading Memories, does that trigger Immortal Phoenix's ability?

Ruling: No, Fading Memories does not trigger Immortal Phoenix. Fading Memories only grants the Temporary keyword to the target unit; the Temporary keyword itself (not the spell) is what kills the unit.

Nuances:

• Kills can be attributed to spells in only two ways: (1) the spell has the Kill action in it, or (2) the unit dies from damage the spell dealt in the cleanup immediately following
• Reminder text in parentheses is not part of the spell's actions
• Spells like Fading Memories and Imperial Decree do not trigger Phoenix because they don't directly kill units themselves