Can you play reaction cards during phase changes, and do you need a chain to exist to play reactions during opponent's turns?

Ruling: You cannot react to phase changes or end of turn itself. During your opponent's turn, you can only play reactions when there's a chain or when there's a showdown and you have focus.

Nuances:

• While you cannot react to phase changes/end of turn directly, you can react to abilities that trigger due to a phase change or end of turn (such as end of turn triggered abilities or start of phase triggered abilities)