Can you react to the Awaken phase?

No, you cannot react to the Awaken Phase itself. The Awaken Phase is a task where the turn player readies their game objects — it doesn't create a chain, and no priority is granted simply because a phase begins (FAQ #10808, FAQ #5566).

Reactions require a trigger that creates a chain, or a Showdown. Since the Awaken Phase is just "ready your stuff" and moves on, there's no window to play anything.

That said, if an ability triggers later in the Beginning Phase (e.g., a Temporary unit dying), that trigger does create a chain — and you can react to that. But not to the Awaken Phase itself.