There is a GitHub repository for PhSim. Currently, there is virtually nothing in it yet. However, as of when this post was created, there is content in the 0.1.0-alpha branch. When version 0.1.0-alpha is completed, it shall be merged with the master branch.

Here is the link:

https://github.com/mjduniverse/phsim

Here is the link to the 0.1.0-alpha branch:

https://github.com/mjduniverse/phsim/releases/tag/v0.1.0-alpha

Please note this is not the PhSim editor. That will not be open source. However, the PhSim library is open source.