The Ubuntu version that xda installed on the phone is the desktop version and not the phone version. The phone specific OS currently only works with some moddels. It bricks most other moddels.
You will not be able to call anything with it if you install the desktop version on it.
That being said, No, there is no "safe" way of flashing any mobile machine. You can however reduce the risks if you know what you're doing and use safeguards like a nand backup.
there is always a slight chance of bricking your system. If that happens you will not be able to put android back on the phone and you'll be left with a very expensive paper weight.
If you're still interested in installing Ubuntu on your phone comment and I'll add the general guide of how to do it to this post.