As announced on the Zend Developer Zone today, there's a new version of the extension for PHP that lets it interface directly with a Solr instance.
The Apache Solr extension is an extremely fast, light-weight, feature-rich library that allows PHP developers to communicate easily and efficiently with Apache Solr server instances using an object-oriented API. It effectively simplifies the process of interacting with Apache Solr using PHP. The Solr extension already has built-in readiness for Solr 1.4
The post lists some of the features of the API the extension exposes (like connection reuse and a simpler interface to response data) as well as a list of supported components.