Apparently our subject's tombstone and numerous other records call him, "Philip," but his will calls him, "Frederick."  All I can figure is that both were his given names, with Philip probably being his call name.

Some online files show our subject as having a prior wife, "Abigail."  This is possibly an error due to misspelling or mis-hearing the nickname, "Appy," as "Abby," then mis-interpreting "Abby" as Abigail.  I've seen it happen before with given name Apollonia.  In any case, the conservative approach here is to assume one wife unless proof of another is unequivocal.

"Apollonia" is a feminized form of male "Apollo," from Greek mythology; other spellings are misspellings.

There is no way Susanna could have been born in 1777 because, at age 48, Apollonia would have been too old.

1.  Marriage Record:

2.  Ellwood Roberts.  1911.  Abstracts of Montgomery Co., PA, Wills & Administrations, 1784-1823.  Genealogical Society of Pennsylvania, Philadelphia, PA (Broderbund CD-209):

Abstracts of Montgomery Co., PA, Wills & Admins., 1784-1823, Will Abstracts...

WENTZ, FREDERICK. Worcester. February 3, 1798. October 31, 1804. 2.415 To wife Appellonia, household goods, interest of 500 pds.  Income of farm, and farm containing 200 acres.  Personalty to be sold, and money divided as follows: to 7 children: Peter, Philip, Catharine, wife of John Knipe, Magdelena, wife of John Erhard Hoot, Nancy, wife of John Ginkiner, Barbara, wife of Philip Stong, Susanna, wife of John Bieber, equally.  Daughter Magdelena to receive interest only.  Daughter Nancy to receive interest of 100 pds. as part of her share. Execs: Frederick Conrad, Joseph Tyson. Codicil dated October 7, 1800. Heirs of daughter Susanna and Magdelena, receive their shares. Execs: Frederick Conrad, John Wentz, son of brother Abraham. Wit: Nicholas Martin, Joseph Tyson, Frederick Conrad.

Some assert that the name, "Frederick," on the will is an error.  It seems more likely to me that our subject's call name was Philip and that Frederick is his first name (Germans go by their middle names as their call names).

3.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).  About a dozen files here containing our subject (husband of Apollonia HARTMAN), all of which call him Philip.