"i can't change the contact poster: Whenever I am trying to change the contact photo and poster of any of my contacts, my iPhone's screen gets freeze and and i am neither able to click done nor the cancel button. Please help"
-------
Troubleshooting a Frozen iPhone App:
I. Start Here: If an App on your iPhone or iPad Stops Responding, Closes Unexpectedly, or won’t Open - Apple Support
II. Perform with a Force Restart:
Is the iPhone frozen, and you cannot get out of this? If so, Force Restart your iPhone.
Refer to this link: Force Restart iPhone - Apple Support
III. Close All Apps, then Try Once More:
If you can get out of this app, swipe your thumb up from the bottom-right corner of your iPhone screen, and then swipe up, one app at a time. Try this once more, with only this app open.
IV. Clear the Caches:
Caches are created for remembrance of application use, so that Apps open quicker, and as remembered. So, clear them. Use my User Tip: How to Clear "System Data" in your iPhone's Storage: - User Tip
V. Update your iPhone:
Use a Computer and Ethernet:
Start with attempting an update. If you cannot use Wi-Fi, then use Ethernet. See my User Tip: Update your iPhone Using a Computer - User Tip. On the computer, you would connect it through Ethernet, going directly into your router. For a Mac (or PC) that does not have Ethernet, this would be the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple.
Back Up First:
IMPORTANT: If you have an option to update, however, then be certain you backup your iPhone first. That way, you will have something to restore your iPhone from should anything go wrong with the update
IV. No Success?
Refer the the following for troubleshooting techniques...