Proper export settings for a mobile-only video?

Hi!
I've got a video which is going to be put into a mobile app, so it will only be displayed on mobile devices. I want the file size as small as possible to reduce the overall app size. What format should I export in for a low file size but still having a great viewing experience on mobile?

I read this article: https://helpx.adobe.com/premiere-pro/using/exporting-web-mobile-devices.html#

But it wasn't super helpful.... because the presets are for YouTube, Facebook, Vimeo, etc.... yet I'm not using these formats.  We're putting the video directly into an app... so it will only play on a mobile device, never on a desktop.