As I'm sure you know, several of us have moved our phone to Pulse8, both from Plusnet and from other high-priced suppliers.
The problem you have is that upgrading to Plusnet FTTC with phone could mean your phone line also goes on to the eighteen month minimum term, and that upgrading to it with the phone at Pulse8 (or anywhere else) would trigger the setup/activation charge that is waived when taking the bundle.
Not helped by the fact it seems asking the chat line or other help service often gives incorrect answers on questions like the first option there.
Kindness isn't going to cure the world of all its awfulness but it's a good place to begin. Daisy Ridley.
My broadband basic info/help site - www.robertos.me.uk.
Domains, site and mail hosting - Tsohost
Connection - AAISP Home::1 80/20. Sync 59500/14989kbps @ 600m. - BQM