MyPhoneExplorer from FJ Software (http://www.fjsoft.at/)
It would be a great addition to Portable Apps.
The software is stable and has been around for about a decade. It is actively developed.
The portable version is included in the installer available from the developer's site, but unfortunately, you currently have to run the installer to create the portable version. That's one reason why it would be such a great addition here.
I do not believe it is open-source. I'm not sure if open-source is a requirement here.