At the beginning of the battle I caught my Phantump, it did the Phantump's Frisk pop-up thing. After I caught it, I looked at its summary and it said its ability was Natural Cure. What happened here...? ._.
A Pokemon cant change abilities unless the Ability Capsule is used on it.
To be honest the comments answered your question, I just wanted to get it out of the "unanswered" section :P.