Clarification on PH vs CP in NK1.5 Phone Number

[SHANNU]

Hello Team,

I have a test story with two guardians (screenshot attached). Both have "Phone Number".

But in the NIST tool example outout message one becomes PH and other CP.

NK1|1|Richardson^Maria^Elizabeth^^^^L|MTH^Mother^HL70063|543 Blount Drive^^Bozeman^MT^59715^USA^P|^PRN^PH^^^406^5557690  
NK1|2|Richardson^John^William^^^^L|FTH^Father^HL70063|543 Blount Drive^^Bozeman^MT^59715^USA^P|^PRN^CP^^^406^5558299  

• On what basis is one phone tagged as PH (Primary/Home) and the other as CP (Cell/Personal)?

• Is this defined by a rule in NK5.3, or is it just an arbitrary choice in the test story?

• For my own test stories, should I explicitly assign PH/CP, or does the tool decide automatically?

Best regards,

Shanmukh