They supply both, but the checker depends on what you are already on.
Zen provide my Fibre (Zen POP) and Phone (via BTW, I guess). Their checker shows
We're currently not able to offer you this service
Your exchange or cabinet is not currently enabled for the service.
You have a new phone line - please wait a few days and try again.
You have a service on your phone line that prevents us from checking it.
You have a non-BT compatible phone line such as from Sky or Virgin.
The BT Wholesale checker works for my phone number