This post may also be applicable to owners of early VW Premium rSAP vehicles because the Bentley electronics are of course actually VW Phaeton electronics.
Bentley now have a dealer fitted upgrade to GTs model year 2003 - 2007 which replaces the arm rest rSAP controls and logic module. this is a 30min fix for Coupe and Spur and 60mins for Drophead. This fix upgrades the car to the post 2007 model year and provides HFP and PBAP. It is compatible with modern phones and claimed to work up to Samsung Galaxy 5 and iPhone 6 but the dealer assures me they have it working fine up to Galaxy 8 and IPhone 8. It supports up to 5 phones and 200 directory entries.
I have previously used the rSAP product and fantastic help from the developer but it is always a struggle when I change phones. For those that want the factory upgrade, which also interfaces with the telephone menu system and are prepared to pay handsomely this might be a solution at £745 from Bentley dealers. I bet there must be a VW equivalent and I also bet it's cheaper.