The name is controversial: this product uses neither the Delphi IDE, nor the Delphi language. Rather, it is inspired by Delphi; maybe it was created with it too. I guess it would have used the Delphi IDE had it not been a third-party buy-in; perhaps it will in future.
The associated library, called VCL for PHP, is meant to be open source; but its home page on SourceForge remains empty at the time of writing.
More when I’ve had a chance to try it out; again, I’d be interested in hearing from early adopters.