You are using phpFox version earlier than 4.6.0? Please refer instruction for this article here.
Requires: phpFox 4.4.0+
Redis is an in-memory database structure, which we have introduced in phpFox 4.4.0+. Our usage of Redis has been focused on lowering the overall load to the MySQL database, especially in the activity feed. On average, each feed you see in your activity stream will have 4 queries. Redis comes in to remove those queries. The main user's dashboard at the minimum would have 40 queries, and with the implementation of Redis, this drops to 1 query which is used to load the specific feed for the logged in user.
Enabling Redis Support
Log into your AdminCP and head on over to Data Cache from Settings menu.
Select Redis as the Cache driver. Then enter the Redis Host & Redis Port information. Select Save Changes.