Manaphy and Dito have to have an egg, and a Phione will hatch.
you need to find 210 Pokemon to complete the pokedex
If You Are Referring To Phione You Must Breed Manaphy And A Ditto To Get A Phione Egg (Which Looks Like A Regular Egg Not Manaphy's). And Hatch Your Phione.
you find all the Pokemon
http://www.serebii.net/pokedex-rs/
you cant
Find all 210 regional Pokemon to complete the Sinnoh Pokedex. Then, talk to Professor Rowan in his laboratory.
You have to go into tall grasses, caves, water, and swampy grasses to find Pokemon. If you capture the Pokemon, they'll automaticly add to your Pokedex. If you complete the Pokedex and you got to Prof. Birch, Prof. Oak or whoever, then you can get a prize.
You can't find it, but you can trade a manaphy egg from Pokemon ranger and put it in the daycare with a ditto.Run around a bit and go back to the daycare. The man should give you an egg which would hatch into phione. ( ditto can be found in the trophy garden after obtaining the national pokedex by using the pokerader .)
He will be in hearthome city
go on codejunkies.com to find out
you can find reshiram in the center of unova when you complete the national pokedex
info on manaphy in Pokemon mansion. trade for manaphy, and breed with ditto. you get a phione