Termux is a terminal emulator application for Android OS extendible by variety of packages.
Download
The version available on Google Play is old and has vulnerabilities. Prefer F-Droid app store. To get the F-Droid, dowload the APK file to your PC and copy it to your phone. Tip: use Dropbox.
Setup
On Termux terminal:
pkg update
pkg install openssh
Set a password for Termux:
passwd
Start the SSH server in Termux:
sshd
Find your Phone’s IP address:
ifconfig
Find your username:
whoami
SSH into your phone from your computer:
ssh -p 8022 username@phone_ip