What do you mean by “maintain”? Are you expecting vault modifications made on this phone to be synchronized with your online Bitwarden vault at some point? Bitwarden currently does not offer any off-line editing functionality.
Also, when you say “online Bitwarden account” are you referring to an account on a self-hosted server?
It’s hard to understand what you’re trying to accomplish, exactly. If you describe your use-case in a little more detail, perhaps you will get additional suggestions.