Microsoft SwiftKey does not have a dedicated minimize keyboard button. Instead, if you slide a finger down the keys from top to bottom, your Microsoft SwiftKey Keyboard is minimized. Alternatively, pressing your phone’s back key will minimize Microsoft SwiftKey.
Please note that if Flow is enabled, you can't slide down the keys to minimize the keyboard. When using Flow, please press the back button on your device to minimize the keyboard.
This gesture is not available for tablet or large screen devices, but using the back button on your device will still work to minimize the keyboard.