You want to send compressed content to browsers that support automatic decompression.
Add this setting to your php.ini file:
Browsers tell the server that they can accept compressed responses with the Accept-Encoding header. If a browser sends Accept-Encoding: gzip or Accept-Encoding: deflate, and PHP is built with the zlib extension, the zlib.output_compression configuration directive tells PHP to compress the output with the appropriate algorithm before sending it back to the browser. The browser uncompresses the data before displaying it.
You can adjust the compression level with the zlib.output_compression_level configuration directive:
; minimal compression zlib.output_compression_level=1 ; maximal compression zlib.output_compression_level=9
At higher compression levels, less data needs to be sent from the server to the browser, but more server CPU time must be used to compress the data.
8.13.4. See Also
Documentation on the zlib extension at http://www.php.net/zlib.