Doesn't matter what "secure" phone app you are using when the keyboard sends everything you type to the "cloud".
(usa.kaspersky.com)https://usa.kaspersky.com/blog/prevent-android-keylogging-and-ime-spying/30145/data about entered text may be sent to the server for personal dictionary synchronization between devices, for machine learning, or for other purposes not directly related to the primary function of the keyboard – such as advertising analytics.
The cloud is just somebody else's computer.
If you really need secure comms, build a small touchscreen device out of an open source micro-controller, and route your communication through a phone or other router.
Everybody should also understand SSL/TLS type encryption and make sure you don't add unneeded SSL certificates to the system to avoid man-in-the-middle attacks.
