Chris Jones has posted more information to his Oracle blog about the caching and other improvements that come along with the Oracle 11gR2 release that can be used in PHP applications.
Oracle 11.2 brought several improvements to Client Result Caching. CRC is way for the results of queries to be cached in the database client process for reuse. [...] PHP OCI8 as a "client" of the database can use CRC. The cache is per-process, so plan carefully before caching large data sets. Tables that are candidates for caching are look-up tables where the network transfer cost dominates.
Like many of the other server-side tools Oracle has to offer, it's pretty simple to enable this caching. Before you had to add a custom bit to your query to tell it to enable the caching. Now it's as simple as setting it up on the CREATE or ALTER for the table - nothing extra for the developer to do.