Hi @BarneyR, I assumed that your only problem was that you couldn't physically fit the handset into the Philips base, which you'd suggested that you needed to do to register to the base, rather than you how you register the base.
However, try this link https://forums.digitalspy.com/discussion/693307/how-to-register-additional-handset-to-base
It's for different handsets but the processes discussed may be of use and you may find the Forum in general a better source of solutions. Good luck.
