I don't believe Plusnet are using CGNAT (at least on the internet) because they have sufficient quantities of IPV4 addresses. Also they had a short trial of CGNAT some years ago but it interfered with a number of protocols.
Since it is possible to generate a IPV6 address from a IPV4 address (but not vica versa) it allows phones to make IPV6 to IPV6 connections.
It will be a very long time before cheap home routers are available for IPV6, even though the pool of available IPV4 addresses will continue to diminish to zero.
"In The Beginning Was The Word, And The Word Was Aardvark."