Yes, it's possible. I used to have an app, but, it seems that an android update removed it on me...
Oh, here's a new one. It's called Printoid. I found it on google's playstore, and it lets you conect to your Octo from outside your LAN. It looks pretty, but I haven't fully tested it yet. There are ads on the free version
Here's another one, it's called OctoRemote. But, it only works inside your LAN. Looks nice
Niether one seems to be able to let me implement GPIO switches so that I can turn my lights on and off, but, there's something in Octoremote that says "controls" that lets you add a script. That might work
And then there's the third option, which is not recommended, which is to put your Octo's IP address into your routers gaming section, and open it up to the internet. But, again, it's a bad idea unless you really know what yer doing and feel safe opening up your printer to potential criminals who would probably want to use the Octopi server to host pr0n and viruses
On the other hand, you COULD get some free pr0n out of it
It looks to me like Printoid is your best option if you want to be able to access your printer from outside your house with your android based phone