Cam a landline phone/fax be connected to a computer - the phone/fax is a Brother Fax-525dt?
That would depend specifically on the make/model and it's specs. I would suggest you drop Brother support and email for that one.
https://www.brother.co.uk/support
The Brother Fax-525dt is a 26yo dedicated fax/copier machine it cannot be set up as a computer printer. As it uses thermal paper it would cost a bomb even if it could be!
@tonyowenwrote:Cam a landline phone/fax be connected to a computer - the phone/fax is a Brother Fax-525dt?
No.
https://www.laserexpressinc.com/manuals/Brother/brother-fax-515-525dt-user-manual.pdf
could this be down to digital voice
You may or (probably) may not be able to get it to work as a fax machine on digital voice - it all depends on how the audio is filtered/compressed. But the only way to have it working as a printer would be to use your computer with a fax/modem, connect that to the fax machine, and hope that the fax machine will still work even if it doesn't detect a dial tone. *Some fax machines will do this if they are set to work alongside an answering machine. But you could well do all this, only to find it still doesn't work!