According to the manual, the handset symbol means that the line is busy. Alternatively, if you look in the problem solving section:
Does the phone line work OK with just a phone connected? Conversely, does the Beotalk work if you disconnect the phone handset?
Could there be a fault on the line? Has your provider changed something (eg gone fully digital)? Are you in UK?
Also have you changed anything with the wiring between Beotalk, Power supply and phone line? It’s worth double checking that the little three way connecter has the correct cables in the three sockets. Remove and fully re-insert (listen for the click) each cable in turn. Maybe try different cables if you have them.
You could also try the setup in a different property if you suspect a line fault.