toots wrote:
I'm not entirely sure why there is a need for ph to have a pick up zone. Ph only pick up when the customer books the fare so surely the driver goes to where the customer is

That is part of the problem I think. The customer is at the taxi rank. Now it may be that over the years that the company has asked it's customers to wait at the rank for the pick up and they don't want to change.
Some councils do have private hire pick up zones, such as Leicester. The police and licensing shut down the area where the clubs are and taxis rank in one place and Private Hire wait in another.