I was also thinking of adding a strap or smaller type little wrist strap to this if someone wanted. I thought that might be nice to carry it with and a bit easier unless you wish for it as is to just put in a bag or purse.
I have an Iphone4 and it fits with a little extra room so I am not sure there would be any difference with the Iphone 5. Are they about the same size? I think the Iphone5 might be a little taller in height and if that is the case the green flap would stretch out a little more but it would still button on its nose. Cotton yarn is stretchy. I hope that helps.