ايكلاود

Binki12 (Google Translated):

iCloud

I lost my iPhone and I did not select the Find My Phone feature and I want to turn off the phone

If Find My is not activated, then you cannot block its use remotely.

If the passcode is not compromised, then the iPhone will be useless to anyone else.

I would suggest to contact your mobile service provider to have them block the SIM.

If your iPhone or iPad is lost or stolen - Apple Support

Mark a device as lost in Find My on iPhone - Apple Support

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