Two ways to zoom in on Instagram on an iPhone
You can change a setting in order to be able to zoom in on a photo on your Instagram feed, or you could simply take a screenshot and zoom in on that.
Sometimes a photo shows up in your Instagram feed with some sort of detail that requires closer inspection. Unfortunately, Instagram does not let you pinch to zoom. There are two ways, however, for you to take a closer look at an image on Instagram on your iPhone.
Method 1: Accessibility setting
If you find yourself regularly wishing you could zoom in on Instagram, there is a setting that lets you zoom in on it or any other app or screen on your iPhone. Head to Settings > General > Accessibility and in the Vision section, tap the Zoom setting. Then, on the Zoom screen, turn the toggle switch on.
Now, you'll be able to double-tap with three fingers to zoom in and out on Instagram or any other screen. While zoomed in, you can move around an image by dragging with three fingers. Double-tap again with three fingers to return to the normal zoom level on your iPhone. You can also change the zoom level after double-tapping with three fingers to zoom in by double-tapping-and-holding with three fingers and then pinching outward. The zoom level you choose will be the zoom level you return to the next time you zoom.
Because this accessibility setting is system-wide, it might begin to feel a bit intrusive if you want to use it only on the rare occasion zoom in on a particularly interesting Instagram shot. You could turn the setting off after using it, or you could skip a trip to settings all together and employ another method.
Method 2: Screenshot
If you stumble across an Instagram image that merits a closer look and don't feel like digging into your iPhone's settings, you can snap a screenshot of an image in your Instagram feed by pressing the Sleep button and Home button simultaneously. Next, head to the Photos app to view the screenshot, at which point you can pinch to zoom to your heart's delight.
(Reddit via Lifehacker)