How to enable zlib compression manually for PHP scripts
PHP Zlib module allows you to transparently read and write gzip compressed files. Thus it is used for serving faster content to the end users by compressing the data stream.
You can easily enable it by placing the following line into your php.ini file:
zlib.output_compression = On
If you are a SiteGround customer you can also enable the zlib compression using PHP Variables Manager in cPanel.