Some words of caution:

• For anything internet related: Keep in mind that you likely are not getting any security updates anymore, even on a custom ROM.

• Also keep in mind that each accu you have in your home rises the risk of fire slightly. Obviously it always depends on the type and age of each accu.

Now some ideas

• Someone on Lemmy wrote about using a phone as Home Assistant box, but I don't remember if it was usable enough (e.g. possible to access usb/sensors/etc)

• You might use them as sensors for Home Assistant, however the accu might not last that long, and/or having them connected to power might not be great for the accu

• Run a media center on it (e.g. Kodi) and cast it to your TV

• Connect some speakers and use them as Spotify boxes in different parts of the house (as it is specifically easy switching devices with Spotify. Maybe there is software for general WiFi speakers)

• Use one to create a smart mirror that displays current information like weather etc

The cameras are usually nice enough for using as a dash cam if you drive. I use one of mine for a media device around the house, kitchen aid etc. I also use an old one for keeping my current one free of boatware, extra apps, and ensuring privacy on my carry phone (by not having anything google or tacking/data harvesting if I can help it).

Outside of that you could look into using them as potential network devices, DNS ad blockers, etc. I haven't looked recently but using one as a casting device receiver for TV would be awesome over a Chromecast or the like. But not sure how those projects are going

My main concern of using a phone as a server is the battery. It'll get spicy after a year of constantly being plugged in, and the phone usually doesn't work without a battery attached.

To run Linux CLI apps, install termux from f-droid and a few of its add-ons. It's nice, you can run sshd on the phone and ssh into it from your computer over USB.

Note that a lot of those older phones are no longer usable as phones, at least in most of the US, because of the 2g and 3g shutdowns and stickiness about LTE/4G. But yeah, they are little tiny computers with cameras and sensors and a screen, etc.

Separate gym phone to track workouts.

Slap DroidcamX on them and use them as webcams or as surveillance cameras. Droidcam is pretty flexible, lets you connect from phone to server or from server to phone or via USB.

Another idea is to use them as MiFi access points on trips abroad. You buy a local SIM card and share the wifi connection as a hotspot or via USB. You can also install Tailscale and use your home server as an exit point for extra security or to access Netflix in your home country etc.

Buy a little controller and install older games to make them into mini gaming consoles. Bonus if you can find a controller that lets the phone sit in the center (I think they make adjustable ones so it should fit any phone).

I give mine away.

Security Cameras

Donate to homeless shelter or men's transitional housing.

I use my phones until the hardware fails, so they're useless. I keep them in a box so they don't end up in landfills.

You don't need to use them, what about selling?

How did u go op? What have you done with them? Also have the same dilemma.

how about using it as a modem or running Transmission and ssh on it? at least that's what I did and it worked well