Odd image behavior on phone

Hi. I am finishing up a website which has a gallery of thumbnail images arranged in (Bootstrap) rows and columns. There’s no coding in them, other than the CSS/Boostrap classes, and the usual Row > Column arrangement (with breakpoints).

Everything is working great on multiple platforms, but today, a friend who is checking out the site on his phone said that when he presses on one of the thumbnail images, it ‘gets bigger’, and a second press causes a 403 error. I have no idea why any of that would be happening, as there’s no coding on the images (or the columns or rows), including any kind of anchor tag.

Any idea why this might be happening? Is this some feature built into the phone browser? Even so, how/why would it be able to isolate the images and have them react that way?

That all said, is there any way to prevent this? At least be able to prevent the 403 code, which makes my website look broken…