Does the PH21 have a liquid Earth?

No, it does not have an LE.
For the type of market this sensor is developed for the LE is often not used. When necessary an earth can be connected on the mounting bracket of the SA11.
Number 14 of the cable can be connected as normal. Provisions have been made in the connector to utilize the reference (13) for diagnostics. Only the glass breakage diagnostics is then available. When connecting a separate liquid earth, as with the pH fittings (FF20/FS20/FD20), all the diagnostics will be available.