How to Force SMB Legacy Mode Version 1 SMB1 In Ubuntu 19.04

A Linux samba server is designed to negotiate with the client the best smb dialect to use between two values: "server min protocol" ( which is set to LANMAN1 predating SMB1 ) all the way up to "server max protocol" ( which is set to SMB3 ). Modification of these defaults by adding them to smb.conf should not be necessary to accommodate a client that can only use SMB1 ( aka NT1 ).

I suspect that the version of the samba client on the Android device may be so old that it's the authentication protocol that is the problem and not the smb dialect. You might want to set those authentication levels with this in smb.conf - right under the workgroup = WORKGROUP line:

lanman auth = yes
ntlm auth = yes

Then restart smbd: sudo service smbd restart

Or do what adasiko suggested and find something newer for your Android.