High Sierra "lock screen" via applescript?

Screen locking has become easier since High Sierra as there is now an explicit "Lock Screen" command in the Apple menu (with a keyboard shortcut to boot). It seems to trigger the same screen lock as a screensaver, but immediately, a far gentler lock than a full return to the login screen.

The question: does anyone know what Applescript command I have to use to call the function? A small app from the App Store called "Bluetooth Proximity Tasker" can run Applescript commands on presence and absence of a paired Bluetooth signal, and I was hoping I could thus use my iPhone as a screen lock enabler.

I'm only interested in locking the screen - unlocking by phone would not be safe 😁.

Any help welcome.