Your phone just has to be in the position your eye would be when it is focused. Just hold the magnifier with the area you want to take a photo of in focus and move the phone till the screen comes into focus. The magnifier will probably have to have a light though.
The magnifier I use has a led strip running around the rim and rather close magnification so I hold it against the camera lens.
Edited by Gincoin43
08/19/2019 2:58 pm