As far as I know, when you take off with the CDU displaying the takeoff page, as soon as you've reached climb power, the CDU should switch into the CLB page, as well as the CLB page, upon reaching cruise level, should switch into the CRZ page, and the latter should become DES page when you start the descent ... (all of these being the active phase, preceded by 'ACT' on the page title)
It doesn't happen by now, does it ?
