Im really upset

I have an iPod touch 4th generation and an iPhone 5.
My iPod still has this amazing app but my iPhone doesnt. My iPod is running the 6.1 software and my iPhone is running the 7.
Is there a difference? Is the app suppose to run on iOS 7 or not? Please help. I love this app

Dudalpg about Percentages - Percent Calculator, v1.9