iPhone has been stolen. Can you lock it?

I cannot lock it. None of the readers of your post can lock it. Apple cannot lock it for you. Only you can do it.

You must have Find My activated before the iPhone was stolen. If Find My was activated, then follow the guidelines in this article published by Apple 👉 Find your lost iPhone or iPad with Find My - Apple Support

Axel F.

Hey there,

Apple can’t access your phone remotely, you can Find your lost iPhone with Find My App .If you can't find it or think it might be stolen, lock it to protect your information and stop someone else from using it See this article to learn how to use Find My app to find your iPhone or lock it ☞ Find your lost iPhone or iPad with Find My - Apple Support

All The Best!