It depends on what FreePBX version you are using.
In FreePBX 17 /var/cache/yum can be completly removed (in Debian yum is not used) and MongoDB packages could also be removed.
I also find a bit strange 3.2G for /var/www/html/admin.
In my FreePBX 17 system, with only open source modules, it’s only 372M.
According with @penguinpbx, in a standard 17 install that folder has only 1.3G (see Drive Partition Layout Survey - #7 by penguinpbx).