I saw this thread but immediately saw that it is not going to work unless you use the phone to intiate a reverse ssh tunnel to a remote host, due to most internet connections being NAT.

My solution which I have finally got working is this:

1. setup an ssh server on a remote host that is on the internet. I run it on port 443 as it's unlikely that it'll get blocked

2. setup key file based login on the server and copy the public key to the phone. This is the fiddly step.

3. create a file in /etc/network/if-up.d/ that contains something like:
ssh -o ExitOnForwardFailure=yes -vvnTNx -p 443 -R 22222:localhost:22 user@remotehost

This way, every time it connects to the internet, it will try to create a reverse tunnel to your remote host. Then if I need to connect to my phone, I do the following command on my remote host:

ssh -p 22222 localhost

hope this helps.