I think you might be looking for statistics in the wrong place.
PBX calls should really be logged in the CRM automatically - if were talking about customer calls. Then the CRM will provide the useful statistics. That's the place to control a sales organization and you have all the other useful metrics there already.
Another thing is support. PBX should log support calls in the help desk system. That's where you want to have the statistics because that is where you can see incoming calls, emails, chat, ticket response times, customer satisfaction etc, etc.
So I don't think it matters what statistics you have in the PBX - unless you're actually looking at the PBX for troubleshooting or something like that.
Look for integration options to CRM, helpdesk etc instead.
When a customer, calls it's invaluable to know that they called yesterday and spoke to Joe about XYZ and so on and it took 1 hour with some teamviewer support.
When you log calls in the appropriate systems, managers get the entire picture of what's happening, not just what calls where made.