iPhone 7plus Pages application - table formulas
Although presently formulas are not available in iOS Pages (version 3.1), if you have a copy of Pages for Mac, the document can be formatted there, share with iOS (either with iCloud, email, AirDrop, etc.) then edit on iOS as illustrated below. The formulas entered using Pages on the Mac will be retained provided one does not overwrite them with other text.

In the example below, the number 317 is changed to 17 thus updating the sum in the footer.