Personalized T-Shirt Pochette
They might be costly or inexpensive. But clever people understand that making pochettes (pouches) out of recycled clothing is preferable. Make them according to your design and wishes. What do you want to put in them, besides your smartphone, wallet, and keys?
Cut the pochette with the center design and neckline intact. Inside out, sew the edges. Start at the sides and work your way up to the shoulders while maintaining an inch gap for the straps. Attach the strap to the pochette after turning it inside out. Leather or braided string are viable choices. Items should be inserted into the neckline via a bit of turn-up on one side of their body (left). All of your nieces will want one!