The BT4600 does have the facility to block all outgoing calls, apart from emergency and any numbers in the VIP list in the phone internal directory.
Page 40 and 41 in the online manual.
It also blocks scam callers, as you can set it to only allow calls from numbers stored in the phone.
Thank you @Keith_Beddoe for your helpful replies.
Yes a phone with this facility may be the best option. There is also a Philips phone which has this feature. I’ll look into these, much appreciated 👍