This one might be a long shot but perhaps worth checking out: There is a Frederick/Fredrick William Philippi that seems to have switched from William to Frederick (Fred) from time to time. He was born 2 Dec 1887.
This gentleman appears on the 1900 Cook Co IL census as 'William Phillip' in index with his father and mother and sister Freda and brother Carl. But his required WW1 registration and required WW2 registration along with his social security record shows he was Frederick/Fredrick William Philippi.
His sister and brother both have birth certs. in Cook Co "Frida Philippi 18 August 1885" and "Carl Paul Philippi 28 Feb 1890" , I did not see one for the William Philippi nor as Frederick Philippi of 1887...as a point of interest might be that this Fredrick Philippi claims on his WW1 registration to have been born Milwaukee, Wisconsin. Parents on the birth cert. are William Philippi and Otelia Ackerman (she has a couple spellings). There is a marriage record for William Philippi to Otelia Ackerman in Cook Co IL 17 Nov 1883)
The gentleman died in May 1963 and is buried in Acacia Park Cemetery in Norwood Park, Cook Co.
The father, William F Philippi born 18 Dec 1850, died 8 Aug 1929 (also buried Acacia Park Cemetery) also looks like he too may have switched between being called William and Fredrick from time to time. If they are the same gentleman both the elder (1850) and the younger (1887) appear together in the 1920 Cook Co census as "Frederick Philippi"
Maybe just a coincidence, but might be worth checking out.
I do see a listing for William F Philippi to Bertha Slapka in Cook Co marriage records for May 1910. According to the tombstone of Edward William Philippi he was born 27 March 1911. And there is a remarriage for Bertha to John J Bachlli on 21 June 1919. Perhaps a review of these actual county records instead of the church records might prove of some worth? There may be a marriage application with the first record that might prove beneficial in assisting you.