When I wear a sundress with no pockets or shorts that don't have deep pockets, I wear this
https://www.amazon.com/Upgrade-Eazy...coding=UTF8&psc=1&refRID=A6F1F9C532V8QTC07T29 under my dress and carry my phone through security. Then I go to the bathroom and pull the belt on top of my dress or leave it under my shirt if I'm wearing shorts and keep it just lower on my waist and stick my phone in it. I have worn it over my dress when going through security but once I had to actually take it off and go through bag check, even though it was obviously not a bag. That was kind of funny since it pulls on so to see me shimmying out of belt was fun, the bag check guy looked at me like I was crazy when I handed it to him and asked why I went through bag check. I did have a small flip type wallet in it and you could see the outline of the wallet so that was why the security guard made me go through. Lesson learned, it goes under the dress and no wallet now. I wore this during the winter this year
https://www.amazon.com/Womens-Inter...coding=UTF8&psc=1&refRID=300794F3FE3R26PK5YWN and it worked well but the phone did tend to pull on it.