The easiest way to download dbphp is to log into the sourceforge SVN repository
svn co https://dbphp.svn.sourceforge.net/svnroot/dbphp dbphp
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Alternatively you can download a complete archive of the source code here
These versions may not always be the most up to date but as SourceForge is throwing a hissy fit and not letting me create release packages they will have to do for now.
Future versions of dbphp aim to include an automatic code generator that can be run against a mysql database and the classes automatically be generated along with the interclass relationships based on the dependencies and foreign keys between tables and columns.
Whilst it would be nice to make dbphp database independent it loses the focus of the project - at the moment dbphp is tiny, only 4kb zipped, and adding multiple database options will cause it to grow into the same kind of bloatware that already exists in other content management systems