The builder is identified in the following sources:

Fiftieth Anniversary of Doylestown Church, Bristol (PA) Daily Courier, Saturday, September 2, 1911, 1, Newspapers.com, https://www.newspapers.com/image/51059946:

Services commemorative of the fiftieth anniversary of the founding of St. Paul's Evangelical Lutheran Church, Doylestown,
for which preparations have been in making for several months, will commence on Sunday morning at 10:30 o'clock,
when the new Bates and Culley pipe organ, which has just been completed will be consecrated with impressive ceremonies.
There will be services all day Sunday and on Monday, Tuesday and Wednesday nights.

"Opens Bates & Culley Organ," The Diapason, October 1911, 1:

Dr. John McE. Ward gave the inaugural recital at St. Paul's Evangelical Lutheran church, Doylestown, Pa.,
on Sept. 4, on the new two-manual Bates & Culley organ. Dr. Ward played the following numbers:
Fantasie on two familiar hymn tunes, Buck; Allegretto, Wolstenholme; Death of Ase ("Peer Gynt" suite),
Grieg; Largo, Handel; "Spring Song," Mendelssohn; Fugue in C Minor, Bach; Bridal Song, Rogers; Cantilene,
Matthews; Humoresque, Dvorak; Grand Offertoire, "St. Cecilia," No. 2, Batiste.

Known from church history web page, Carnegie Foundation research by Andrew Henderson and a contemporary newspaper report, none of which identify the builder:

"In the ensuing years, numerous projects were undertaken to expand and enhance the worship space. A new hand-carved oak altar was built in 1896, and is still in use today in the narthex of the current church building. In 1911, a new pipe organ was installed, funded partially by noted philanthropist Andrew Carnegie."
-- church history page

"CARNEGIE GIVES PIPE ORGAN Doylestown, Pa., Feb. 2-It was announced in St. Paul's Lutheran Church here last evening by the pastor, Rev. Charles W. Jefferis, that Andrew Carnegie had written a letter in which he promised to donate $750 toward the pipe organ fund of the church.

The congregation was highly elated at the good news, as the donation will enable it to install an organ as a memorial of the fiftieth anniversary of the church, the celebration of which will take place next fall."
-- Coatesville Record, Thu, Feb 02, 1911 · Page 2

St. Paul’s Evangelical Lutheran Church, $1800 ($750 provided based on original proposal) – but no instrument details provided, unfortunately.
-- information from Andrew Henderson via email January 5, 2026