User blog comment:Miskos3/Fairy Tail Episode 249: Tartaros arc: The Celestial King vs. The Underworld King, Review/@comment-180.191.130.34-20150906035140/@comment-7418318-20150906072201

Maybe.

But it's also possible that there are other ways to summon the Spirit King than breaking a key, only that Lucy didn't have the means in this situation.

One quite popular fan-theory is that possessing the whole set of Zodiac keys allows summoning the CSK, though so far that's baseless speculation with neither evidence for or against it.

And as we've seen when Lucy saved Loke, the CSK also has the ability to come to the Human World under his own power under certain circumstances, so he might not have been summoned at all. But on the other hand Mard Geer said that he hadn't expected someone could summon the CSK so this is a bit unlikely.