

What I ask myself here is why I should have unused phones lying around in the first place?
If I somehow think constantly wasting money on a new model just because there is a new number written on its packaging is worth it, I would not actually think in terms of reusing old hardware.
If I am however thinking about using hardware instead of just throwing it away while still functional why wouldn’t I use a phone as anyone else as a phone?


Security through obscurity never works, so changing you SSH port does barely anything
… for security that is.
What it does is keep a lot of automated bots from spamming your server. No, they don’t have any chances to get access when key authentification is used (and they won’t try either… most go for the incredible low hanging fruits like admin/admin user/password sets), but they can become a strain on your own ressources.
What actually helps (and is usually configurable with any firewall) is rate limiting access. Just blocking someone’s access for 10 seconds after a failed attempt will make absolutely no difference for you but a big one for those spammers. Now add some incremental increase after multiple fails and you are perfectly set.
PS: 53 is the standard port for DNS when your server operates as such.
PPS: Don’t use it. People should really let that stuff die and exclusively run encrypted DNS (via TLS, HTTPS or Quic…)