In the good old days, accessing the files in an Android phone was easy. Just plugging via USB port was showing the phone as an external drive. Nowadays, as we need more secure and reliable protocols, it needs new commands to mount them as disks.
I'm using jmtpfs for mounting phones. First install it via
sudo aptitude install jmtpfs
and make a directory in your \$HOME like
then, after plugging the phone, type
should mount the phone under the directory. Note that, if you have a password/pattern to unlock your phone, you need to unlock your phone. Otherwise when you cd \~/myphone it will say Input Output Error or something similar.
After you unlock the phone, you can use this directory to use your phone as an external disk. Then when you want to finish and unmount, simply type
fusermount -u ~/myphone
and your phone is ready to be unplugged.