There are a few things you can do to help see through white shirts on your iPhone. One is to use a mirror or other object to reflect the light back at the person you are trying to talk to. Another is to take off any sunglasses or other sunglasses that you may be wearing and place them on the ground in front of you so that the light from your phone can shine through them. Finally, try using a speakerphone or headphones so that you can’t hear what the person is saying and just listen for any sound that might be coming from their shirt.
