That is the same thing. The messages were stored on your phone never on any "account". The desktop was only ever a mirror of the phone. This is explicitly how Signal works. WhatsApp works the same way.
If you did not delete the Signal directory on your phone then there should be some old backups with your messages there. These will be encrypted so you will need to original password to unencrypt them.
If you did not delete the Signal directory on your phone then there should be some old backups with your messages there. These will be encrypted so you will need to original password to unencrypt them.