apt - How to install Brosix secure instant messaging on an Aquaris E5 Ubuntu phone

I have already installed the Brosix .deb app on my Kubuntu 15.04 laptop without any problems.
I copied the app to the downloads folder on my Aquaris E5 Ubuntu touch phone, downloaded the terminal from the Ubuntu store and used the 'sudo apt-get install' command in an attempt to install the app.
I receive the following message(s)...

W: Not using locking for read only lock file /var/lib/dpkg/lock

E: Unable to write to /var/cache/apt

E: The package list or status file could not be parsed or opened.

Does anyone know how to sucessfully add Brosix to an ubuntu phone?

I chose Brosix due to the security aspect and the fact that it can be installed on all platforms, so I'm really hoping there is a solution.

Thanks in advance for your help.