Some easy steps..
Your ubuntu and android should be connected to the same wifi.
1. Install FTP Server App on your android smarthphone
2. Intall Filezilla on ubuntu
3. Start your FTP server at your smartphone. This gives you IP, user, password, port.
4. Conntec from FileZilla to you FTP server
You can transfer now whatever ypu need on any direcition.
P.S. There is a micro flag