Playing Minecraft together and not sitting next to each other?

A friend and I would like to play Minecraft together (with the cell phone) while we're not sitting next to each other, so we do not use the same Wi-Fi. I saw that this should work with the Xbox app, only I don't know how, can someone please explain this to me?

It's been a long time, but I'm pretty sure that you have to log in to Xbox live or whatever that means, your friend also needs Xbox live and afterwards you only have to add "Adden" or Add as friends in Xbox live. And after that it should actually work. So if one is in a Minecraft world, the other should be able to see and join it.

Thanks, but it never says join. But thanks anyway