This won't be a post for people that already have dedicated server hardware, unless they find something theyd like to run off an android phone specifically.
But anyways, more people than ever have and old spare, but relatively powerful, android phone laying about. I'm talking 2-4+ gb of ram and 32gb+ of storage. Usually these devices end up in a drawer, but in an age of dystopian tracking and company overreach, such a device can be an extremely useful and low power draw tool that can improve your security and experience on the web. And it also has its own battery to boot lol.
If you're wanting to do something like this you should definitely consider finding a custom android rom with more care for security and you will need to root your device. But with a rooted device you then get access to a range of tools. You will want to install magisk through the bootloader as well as termux and termux boot from within fdroid (its important you get the two of them from the same source).
USES/SERVICES
With all of these theres now a few options that I can confirm all work on android armv8 devices.
0: To set up most of these services to boot on launch you can either use magisk boot scripts in /data/adb/service.d/ iirc, or you can use termuxboot scripts placed in /data/data/com.termux/files/home/.termux/boot/
1: You can run an instance of Adguard Home on your network that will have enough resources to handle quite heavy lists. You will need to import ssl certificates to properly get it working but otherwise the armv8 binary works well. Adguard home can then be set as your network's dns address. Adguard home has lists for threat protection, to malware, to ads etc.
2: Adguard is good for security but you can experience even less tracking and control by pairing it with an instance of Unbound dnsrunning on the same device. Depending on storage you can store larger dns caches which will stop dns providers from tracking every dns lookup you do.
3: This one is more optional dependent on the person but i use and love it. Searxng is a privacy focused metasearch engine that can aggregate a bunch of data from tons of sources, depending on which sources you enable. It can be used to replace your current search engine such as duckduckgo and can gather anything from torrents and apks, to music, videos and pictures, and my favourite which is its equivalent to google scholar. All in one search engine. Its recommended to disabled certain sources for speed and I would recommend disabling brave search as a source for example because they're scummy. For Searxng it will be required to create a virtual environment with the correct python dependencies and I've had to run it through termux rather than the other two which can run even through an adb shell.
4: Memos is a nice note taking webapp and its my personal choice to use but other similar calender or note apps are a good option if you wanna self host something like that. Can be ran through an adb shell or magisk boot script.
5: Others things you wanna try!!!
An android phone is just a Linux computer and if theres services you've wanted a pi to run or a server in general then theres a pretty good chance you can get it running on your power efficient android phone thats just already laying around!!
Heres some more ideas ive planned to try but not gotten to yet/haven't finished:
-Samba drive to sync and back up your boot drive
-Aur build server to pre compile different large packages to be installed to my pc without building them on the computer itself
-openvpn proxy to run downloads through a protonvpn account for download managers that dont support password authentication (a surprising amount of them tbh)
-Invidious instance, a youtube frontend that doesn't count as actual page views. This allows you to boycott YouTube in regards to data they can show advertisers, while still allowing you to privately subscribe and watch creators you like. It also keeps you from being tracked by your YouTube account while giving you access to better/more consistent resolution tools as well as automatically removed ads. Youtube sponsorblock extensions can also be set up to work with invidious so you don't lose much at all switching.