Can Apple deactivate an iPhone with a serial number?

If you had Find My turned on in the phone before it was lost, it is already useless (if you don't respond to any scam messages that appear to be from Apple and divulge your Apple ID password). See: Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Apple doesn't take reports of stolen devices but you should report it to your wireless carrier. See the information in If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

If you didn't have Find My turned on in the phone before it was stolen, see: If Find My iPhone or Find My iPad isn't enabled on your missing device - Apple Support

Click here for information. Neither Apple nor anyone else can block or locate units based on the serial number, unless someone happens to turn one over to them.

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