Upgrading your phone from Ubuntu 13.10 (Saucy Salamander) to Ubuntu 14.04 (Trusty Tahr) might cause you to lose all your data.
A user has pointed out the upgrade process from one operating systems to another, with the normal phablet-tools, will cause the loss of all the data on the phone.
“I upgraded my phone to the trusty image today using phablet-tools, but got hit with a bug that resulted in losing all my data. (bye bye pictures!) Although the best way to do the upgrade was mentioned on the list, I noticed it too late,” said Marc Deslauriers on the official mailing list.
There is a way around this problem, at least until this bug gets sorted out. Either use the adb shell system-image-cli -c trusty -b 0 -v command, or install the updated phablet-tools saucy package from the ppa:phablet-team/tools PPA.