Phione is a special event Pokemon that was only available in Pokemon Diamond, Pearl, and Platinum through a specific event. It's not obtainable in the regular Pokemon Rumble game.
However, in the game Pokemon Rumble Blast, you can obtain Phione by completing the "Phione's Wish" event. This event was available for a limited time, so you'll need to check the game's news and announcements for potential future events.
It's important to remember that event Pokemon often have limited availability, so keep an eye out for opportunities to get Phione if you're hoping to add it to your collection.