How to remotely deactivate a lost iPhone?

Use Find My, you can erase the phone, but do not remove it from your Account unless you want someone who finds it to be able to use it.

Erase a device in Find My on iPhone - Apple Support

Also contact your cellular provider along with more information here:

If your iPhone or iPad was stolen - Apple Support

Marking it as lost will deactivate all cards and still allow you to see it on a map when it makes an internet connection. It is still protected with your Passcode and the device cannot be reset.

Use Lost Mode in Find Devices on iCloud.com - Apple Support

See what you can do here --> Find your lost iPhone or iPad - Apple Support