There is a workaround this problem and it's pretty simple
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.