As the other poster suggested, you don't have the English language version of the app.
Also, while iTunes can handle higher rez music files, the iPhone can only handle up to 44.1/16. (Thus if your original file was 96/24, you will need to convert it to an Apple playable format that is 44.1/16 which is CD quality).
If you Flac file is 44.1/16 then a direct conversion.