You can use the browser on your phone to go to https://steemitwallet.com and click "Keys & Permissions". If you only know your master key, then you have no choice but to use it to log into https://steemitwallet.com once. When the site reveals your other keys, write them down and store them carefully like you store your master key. You'll only have to do this once.
Always make sure you have spelled the URL correctly! Never log into any site that does not begin with https. You don't want any password ever to be sent over an unencrypted connection.
There are ways to generate your other keys from your master key offline but that requires installing certain programs on your desktop or your laptop. If you have neither, I guess you'll just have to do it online.
And please store all your keys in a safe place. If you lose your master key, it will be impossible to recover your account if you get hacked.