How to figure out source of reflections causing glare?

recently I’ve started making videos and issue I face when recording them is the glare I have on my white boards:
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I drew a picture of my source and subject (the white board):

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More details: The light bulb I am using is a wix light bulb and the camera is just the rear camera of a Samsung galaxy s7.

Initially, I was of the opinion that the spot was simply due to the light source I had but I fixed the glare problem in an ad hoc way by noticing that as I raised the height were camera, the ‘light spot’ on the board raised height as well.

This led me to think that perhaps it is due to a reflection of the white board with some part of the surface of phone. I tried covering the bulk of the phone and concluded that it’s definitely not the bulk, a possibility was the camera it self but I couldn’t figure out how to test for it.

Snell’s law seems can’t be directly be applied to figure out where the bright spot is from because there are many sources which can cause the same bright spot.

This leads me to my question, how do I figure out what is causing glare, systematically?