Secure ShellFish: SSH Terminal and File Access for iOS
Secure ShellFish is an SSH client for iOS and macOS whose distinguishing feature is integrating remote servers into the Files app.
Files integration is the differentiator
Plenty of iOS SSH clients give you a terminal. Secure ShellFish additionally mounts remote servers as locations in Files, so any app that can open or save a document can read and write directly on your server over SFTP. Editing a config file in a proper editor, or saving a photo straight to a server, stops requiring a laptop.
Terminal features
Hardware keyboard support with sensible modifier handling, key-based authentication with keys stored in the Secure Enclave where supported, port forwarding, and widgets for running saved commands.
Key management advice
Generate a dedicated key for the device rather than importing your main one. If the phone is lost, you revoke one key on your servers instead of rotating the key you use everywhere.
Alternatives
Termius covers more platforms with team-oriented sync; Blink is the other well-regarded iOS terminal. Secure ShellFish is the one to pick if the Files integration solves a problem you actually have.