I am struggling with this myself - Note that there is a no-longer (in 2016) updated version of the phablet-tools package in trusty/universe. Use the PPA instead.; you need to download them from here; https://launchpad.net/~phablet-team/+archive/ubuntu/tools/+sourcepub/5673076/+listing-archive-extra - The trouble is I do not know where you should extract them to......
UPDATE
I spent lots of time trying to make this work; in the end I gave up - got an old machine, installed precise (which has Phablet-tools etc in its universe repository) - or does it? - I am still struggling with the phone installation
Update 2
Still struggling with this; The instruction page here https://developer.ubuntu.com/en/phone/devices/installing-ubuntu-for-devices/ says Note that there is a no-longer updated version of the phablet-tools package in trusty/universe. Please use the PPA instead.
So I installed Precise on an old machine
however; here it says phablet-tools for precise have been deleted.
It seems whatever I do I cannot achieve this. I will keep digging and post an update.
I could do with a plan B because this is driving me nuts...
UPDATE 3
Went back to try with Trusty; in trying to install phablet-tools as suggested above I get
The following packages have unmet dependencies.
ubuntu-device-flash : Depends: click-ubuntu-policy but it is not installable
Depends: ubuntu-snappy-cli but it is not installable
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