When your phone is taking a reading you should hold it the way that feels most comfortable for you but ensure that you are able to cover the phone’s camera and flash and also keep it as still as possible.
Here’s our recommendation…
Hold your phone in your left hand and cover your phone’s camera and flash with your left index finger.
If it helps, bring your right hand in underneath your left hand to act as support
Then bring both hands towards your body so you can hold it as steady as possible
The most important things are to rest your phone’s camera and flash on your finger, rather than gripping it. This way the phone can take the most accurate reading.