Please tell me where I can download Fairy Tail the movie ending song-Zutto Kitto(Aya Hirano) to my mobile!

You can find all Fairy Tail songs (OP, ED, Character Songs, etc.) here:

link
Just click the download link and wait to skip the ad.

If you just want that song:
link

These will download it to your computer. Then all you have to do is connect your mobile to your computer in anyway that suits you to transfer the file. Cable, bluetooth etc.
I'm hoping your phone is not very old and is capable of doing this.