My iPhone isn’t updating

Do you see the "double loop" in the upper right-hand side of your iPhone? That indicates that it is connected to a Personal Hotspot from another phone. As such, it will not be able to update/upgrade iOS with this type of connection. Try connecting your phone directly to a Wi-Fi network (with Internet access) or to a computer that does.

You can't use a Wi-Fi hotspot, you need to be connected to a Wi-Fi signal coming from a router.

You also need at least a 50% charge on your battery. Plug it into a charger, charge it to over 50%. Better yet, leave the charger plugged in while updating.

Also, the download will not occur if your battery power is less than 50%. Charge the phone to 100% before you try the download again.