Edward Snowden failed force journalist Glenn Greenwald to use PGP tool to secure each other communication. It was so complicated and confusing!
Sometimes you need use keys that are not available on keys servers, then you can copy public keys files between your computer and iOS application with iTunes File Sharing.
Many apps store the app's settings in the main "Settings" icon on the iPhone's home screen. Click on the settings icon and scroll down the list of apps at the bottom of the settings page. Then click on the app's name within settings to manage the settings for that app.
Keybase.io - use keybase username in recipient field
Public keys servers - you can reach any recipient, which published his public key on servers