I think the standard definition of a Call Centre is an office within a large organisation that employs staff to either sell its products directly, or to respond to incoming sales enquires, and also to deal with customer complaints. Thewy usually employ massive amounts of staff, and if they are anything like the call centre in ths building, they have a similarly massive turn-over of staff and a hige sick absence problem.
So no, I don't think your central plumbers' work routing team are really a Call Centre.