This app was mentioned in 1 comment, with an average of 2.00 upvotes
EpocCam works really nicely for my ipad, but I haven't tested it on my android phone yet.
https://play.google.com/store/apps/details?id=com.kinoni.webcam&hl=en
To put this on OBS, just create a scene for a window and select the window for the webcam screen that is displayed on your computer when you download the required software.