The Vita version is for Japan only, click the Japanese version of the site to see it blinking hopefully at us. Given the western love of most things Final Fantasy, raw economics can be the only reason Square Enix is coding an English version for smartphone.
UPDATE: Hold that thought Square Enix's EU Twitter account is asking for feedback on the English version. I'm not saying my angst made any difference, but go comment on their blog to have your voice heard.
Perhaps if there's enough interest they will see the error of their ways and let us play too!If you'd like to play Adventures of Mana on PS Vita let us know on the SE Blog!— SQUARE ENIX EUROPE (@SQUARE_ENIX_EU) February 5, 2016
Their message reads, "Thank you for all of your comments on a PS Vita edition of Adventures of Mana. We’ve been listening to your feedback and because of your passion for the game, we’re going to look into making a PS Vita version of Adventures of Mana for the west. We can’t guarantee we’ll be able to make this happen but we will see what we can do."