How do I disable my lost iPhone?

Inform your wireless provider - they can disable your iPhone.

Here are 2 links to Apple's advice about a stolen/lost device:

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

Find your lost Apple device or AirTag with Find My – Apple Support (UK)

Click here for information; all of the options for disabling it are available through Find My or by asking your wireless carrier to blacklist it. The people on these boards are mostly other customers and can't do that in any case.

(254166)

_bdg20 wrote:

My iphone got stolen, please disable my phone

ref:

If your iPhone, iPad, or iPod touch is lost or stolen

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

You can sign into any web browser and go to apple.com, iCloud.com, or Findmyphone.com use your Apple ID login and disable , reset or set lost phone alerts directly yourself. Additionally you can track the iPhone location if you have had it on. Then you can even ping other IOS device users to sort of follow the phone and or find phone and other smart devices you have tagged! I am absent minded and often lose my iPhone/iPad. I always find it or someone returns it to me! Good luck! ~ Lucious L.