@raffy_m, the URL, username, and password that you see under Server settings are used to connect your Collect android app and the server (your KoboToolbox user account).
The Username, Phone number and Email address that you see under the User and device identity are the metadata that will be sent to the data along with the other information your collected for the project. This metadata should provide additional details of who collected the information for you. It should also be helpful if you wish to ensure Data Quality Assurance. To collect this metadata you will have to activate the same through your survey project settings.
I see, So if you do not fill up the username field in User and device identity, it will result in having a blank field under the username column when the data is downloaded. The username that you use to connect to the server is not used in the metadata.
Also, you could use a different username in User device and identity from the one you use to connect to the server…