Here are the only three William Phillips marriages that I can find in Co. Down:
21/2/1860 William Phillips to Henrietta Wilson in Saintfield Church of Ireland, Saintfield Parish
13/8/1852 William Phillips to Catherine Conovan or Connoway in Tullylish C of I, Tullylish Parish
25/11/1856 William Phillips to Alicia Clawson in Seaford Presbyterian Church, Loughinisland Parish
I can only find children born to William and Catherine after Civil registration
Catherine in 1867 and
David in 1870
and since they married in 1852, by the law of averages, they would have had children before civil registration
In Griffiths Valuation 1863 there is a William Phillips listed
Hopes this helps in some way. RosemaryJoan