A free program for Android, by Banana Studio.

SSH/SFTP Server – Terminal is a powerful application that allows you to run SSH-based servers on your phone. The application is designed to run on Android devices, and can be used with any kind of Wi-Fi network, including Wi-Fi networks that are shared by other devices. It is designed to allow you to access your files and send them over the network in an encrypted manner.

To use it, you will first need to set up the application and configure it to use your phone’s Wi-Fi network. You will need to enter the IP address of the device that you want to access and set up the user account.