Staff can't comment beyond what's in the manual, but if you read Section 1.3.1 https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v232/en/flu_udf/flu_udf_DEFINEMacros.html%23flu_udf_IncludingUdf_h and use a bit of lateral thinking you may find more information. As the second macro isn't in the manual I can't say much.
As a general comment, c & t typically are cell and thread. Whether you need to define the phase domain will depend on whether the value is kept at the phase level or mixure level: that may be model dependent.
You are navigating away from the AIS Discovery experience