So an itunes code generator was just received by me and I used it using my iphone. A song was purchased by me, and I was thinking how could I know if it's using the gift card to buy tracks, or my credit card using my phone?
Based on Apple "Gift certification, allocation breaks, and prepaid credit card are utilized first. .If you've number free tune credits or present certificates, prepaid cards, or allocation credits, your charge card is charged for the tracks you buy."
Therefore more straightforward to check always your breaks outstanding before and after getting items on itunes code generator
For more info visit: http://www.lmgnc.org/itunes-gift-card-generator-get-free-itunes-codes
So I think once you put in the code it automatically uses that, in the store, if you look somewhere at the top of the screen, forget where, you can see the amount you have to spend from your gift card, and it deducts it each time you download a track so you always see how much you have left.
that's how it's worked for me on the desktop version, just noticed you said phone, but I think it works in the same way on iOS. It just automatically uses the code.