You can still run the app on an iPhone 5S building it for 32-bit only, because the iPhone 5S will run existing 32-bit apps. Many apps will need to wait to start building for 64-bit until library vendors update their code to fix 64-bit issues, and in the case of static libraries to even include a 64-bit build of their code.
There's not really any reason you would absolutely need your code to run in 64-bit right now that I can see, and even if you did, you couldn't guarantee the stability of the third party libraries you're using. So I would suggest you, for the time being, stick with building 32-bit only, and it will run just fine on an iPhone 5S.
If you for some reason did absolutely need to be able to build your app for 64-bit, you'll either have to get the library vendor to update their code, or you'll have to remove it and write your own code to handle what theirs was doing.
EDIT:
To fix this exact warning, in the spots where it has %d, replace them with %lu.