Christopher Jones talks today on his blog about a bug he's just corrected and integrated into the release of the Oracle Instant Client that lets PHP correctly take advantage of the temporary LOBS functionality.
When PHP is done with the temporary LOB, it needs to tell Oracle to destroy it. If this isn't done, then the temporary LOB will hang around using DB space until the connection is closed. I just merged a fix worked on by Krishna Mohan and myself for bug 43497.
Example code is included showing two instances of its use - a normal use that frees the memory correctly and the other showing how to create the temporary lob to hold the data as needed.