

As said in another comment a bare metal Debian install likely wouldn’t be very smooth, or you’d have to run it within Android. Alternatively, if you want to run Linux directly on the phone you could try postmarketOS https://wiki.postmarketos.org/wiki/OnePlus_5T_(oneplus-dumpling)
I can’t help as much with the exposing outward (I’m a basic bitch and just use ddns to expose mine since I can’t get a dedicated IP) but a separate vlan with rules to allow your primary vlan devices to see/talk to it, and block it to be able to see out of it’s own VLAN, would definitely be recommended.
Terminus is nice and has a lot of platform options. Ive used on an old ipad in the past. If you have several machines, I highly recommend servercat. Works wonderfully on iphone, ipad, and Mac. It also has options to write and store commands to easily send out to any number of devices with a taps/clicks.