Just go into the iTunes app and scroll to the bottom of the page. Any gift card credit on your account will be displayed under your Apple ID. If it isn't there or the amount is incorrect, tap on your Apple ID and sign in to your Apple account. The correct balance will now be shown. BTW, this balance is a collective balance, the total value of all gift cards credited to your account is displayed, without the values of gift cards being displayed individually.How can I use iPhone to find iTunes gift card balance.