Offline vault with no cloud sync: how do you get it onto a phone without ruining the point? Self-hosted

You have not solved it because it is not solvable in the shape you want it. Two devices that both accept writes and are not connected will diverge, and every fix is either a sync protocol or a rule about which copy wins. What worked for me was demoting the phone to read-only: it gets a copy after every desktop change, and any new entry goes in on the laptop later. Slightly annoying, entirely consistent, and no conflicts in three years.

Worth separating two fears that usually get bundled. "I do not want my data in someone else's breach" is addressed by the vault being encrypted with a key the provider never has, which is true of the mainstream ones. "I do not want to appear in anyone's dataset at all" is a different requirement and only self-hosting satisfies it. Decide which one you actually hold, because the first is much cheaper to satisfy than the second.

Sync it over your own network only. A file-sync tool that talks device-to-device on your LAN gives you convergence without a third party holding anything, and it will happily sit idle until both devices are home. It is not zero effort to set up and it will occasionally need a nudge, but it removes the manual-copy divergence you are describing.

Backups matter more than sync here and I learned that expensively. Offline means nobody else has a copy, including you, when the drive dies. Three copies, two media, one of them somewhere else, even if that somewhere else is an encrypted file on a stick at your parents' house.

Offline vault plus a strong passphrase plus a hardware key file on a small USB stick you actually carry. The key file being separate from the database is what makes the paranoia proportionate rather than performative, since a stolen laptop then gets an attacker nothing.