Your friend shared an awesome image on Instagram, but it’s a bit too tiny? Unfortunately, Instagram does not let you zoom on iOS. But Redditor kaidangku suggests you can bypass this by using a built-in setting on your iPhone/iPad/iPod Touch.
The Accessibility settings of iOS have an option to enable Zoom, letting you magnify any screen. Go to Settings > General > Accessibility > Zoom and turn it on.
Double-tap the screen with three fingers to zoom in, do it again to zoom it. On the first double tap, you can also pinch out to zoom in more.