Simply:

Plug in the phone via USB.

At the command line:

dmesg | tail

You should see a line like:

[18373.951006] sd 2:0:0:0: [sdb] Attached SCSI removable disk

In this case, the Nokia phone has been connected as drive sdb.

Now, check that it is shown with:

cat /proc/partitions

If you can see it all good, now you have to mount it.

In my case:

sudo mount /dev/sdb /mnt

And there you go!