Chaos Lord doesn't have Phase Dragons in his deck. If a Phase Dragon of any kind appeared on his side, it was a result of mutation. A mutant has a random +X/+Y to the base creature stats and a random ability. So the Phase Dragon that appeared must have had a different ability.
Hmmm...it being the result of a mutation would answer it. I thought he mutated it a few turns later, but I may have been mistaken and he played another creature and mutated it right after so I didn't catch it.
It would be nice to have a log of what cards were played/actions taken for the last turn or two. There are times when things just happen and I have no idea why. For example, a creature disappearing could be due to Reverse Time, Eternity, a failed mutation, etc.., and it's not always clear what happened, so it would be helpful to look and see "[Player X] used Eternity to reverse time on [Creature 1]" or "[Player X] plays a Reverse Time card on [Creature 1]."