Amazon Fire Phone question

Anyone remember these?

I have one and I’d like to press it in to service to play Audible (and other) audiobooks.

The problem is, it’s a very old phone. And I’m not all that good with phone-y things.

Can anyone point me to how to get the Audible app on there? Preferably without wiping the original OS, because the pseudo-3D effect is cool. But if that’s the only way, so be it.

In theory, there should be a configurable option in the Fire OS settings to allow you to install applications independently of the Fire app store.

After that, it becomes a question of how to find someplace that can make apps available for web download outside of an app store. There are several, but I don’t have any recommendations. I will say that the extreme age of the operating system (equivalent to Android 4.x Jelly Bean, no later than 2013) will be a huge limiting factor as to whether an app will install on the device.