Can I use a reaction during my opponent's phase change (specifically during their End phase)?

Ruling: You cannot use a reaction during a phase change on your opponent's turn. Phase changes do not give priority and are not valid triggers for reactions.

Nuances:

• You would need a showdown or a chain to be created in order to react
• If your opponent performs an action during their End phase, priority would pass to you to respond to that action
• You don't have priority on your opponent's turn during phase changes