In a showdown, if the defender kills the attacker's unit triggering Phoenix, and then the attacker kills the defender's last unit before Phoenix resolves, can Phoenix only be played to the defender's base (assuming they don't control another battlefield)?

Ruling: Yes, if the defender kills your unit triggering Phoenix, and you then kill their unit on the battlefield before Phoenix resolves, Phoenix must be played to their base or another battlefield they control.

Sequence:

• Defender kills attacker's unit, triggering Phoenix
• With Phoenix trigger on the stack, attacker kills defender's last unit on the battlefield
• When Phoenix resolves, the defender no longer controls that battlefield
• Phoenix must be played to defender's base or another battlefield they control