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There is DroidCam which works with an Android phone and Linux. The set-up is straightforward and it works great.

Mine keeps disconnecting after a few seconds. DroidCam has never worked well for more than a minute for me.

Wish there was a FOSS alternative.

Not FOSS, but try also IP Webcam, it gives you a MJPEG stream and you can set it up on your computer.

I use https://github.com/agarciadom/ipwebcam-gst as a way to turn the MJPEG into a video device.