digital – What are these lines in photos when viewed zoomed in on iPhone?

I take photos on my Canon (It happens on both my Canon EOS Rebel t1i and my Canon EOS R) camera then download them onto my iPhone. Then when I zoom in close enough, there are these invisible lines on the image (when you follow them along they form a 3×3 grid on the image).This happens in every single image that I download from my camera to my iPhone. What are they, and if possible, how can I fix them?



Half-Way Zoomed In:

Half-Way Zoomed In

Fully Zoomed-In:

Fully Zoomed-In