Why my iphone is consuming so much mobile data

You may find it helpful to turn on Low Data Mode to restrict background network use and save cellular and Wi-Fi usage.

You might want to use Low Data Mode if your cellular or internet plan limits your data usage, or if you're in an area with slow data speeds.

To do this go to Settings > Cellular > Data Mode > Turn on Low Data Mode

You can find more information in this guide here: Use Low Data Mode on your iPhone and iPad - Apple Support

~Hope this was helpful