You are using phpFox version earlier than 4.6.0? Please refer instruction for this article here.
Requires: phpFox 4.4.0+
With phpFox version 4.4.0 and later, Admin can choose the data caching system that is appropriate for their site. Available caching systems in phpFox are:
Admins can edit their system cache directly from the AdminCP > Settings > Data Cache
Select your preferred data cache system you want to apply to your site.
If the driver cannot work based on their server/settings, it always falls back to the flat file system.
The settings for the cache are stored in the database, but in case the admins cannot access their site because of their cache driver, these settings can be found in a PHP cache file, located at:
If this file does not exist, we fall back to the Filesystem cache.