Yankee Stadium (both the one opened in 1923 and the one opened in 2009) has called the “Home Office of Baseball” or “Baseball’s Home Office.”
   
“John Smoltz said Yankee stadium is a cathedral to baseball. The stadium has also been called baseball’s home office” was posted on the newsgroup alt.sports.baseball.ny-yankees on June 20, 1997. “Don’t compare the Yanks with any other franchise, they are in a different league. As they say, the Bronx is the home office of baseball” was posted on the newsgroup alt.sports.baseball.ny-yankees on July 10, 1998. “Baseball’s home office, Yankee Stadium” was printed in The Spokesman-Review (Spokane, WA) on October 10, 2000. “The Home Office of Baseball, or the Baseball Cathedral, or the House that Ruth Built, or, if you prefer, Yankee Stadium” was posted on the newsgroup alt.culture.ny-upstate on October 20, 2003.
 
Other Yankee Stadium nicknames include “Big Ball Orchard in the South Bronx,” “Bronx Bandbox,” “Bronx Toilet,” “Cathedral of Baseball,” “Coors Field East,” “Launching Pad” and “The House That Ruth Built.”
 
     
Wikipedia: Yankee Stadium (1923)
The original Yankee Stadium was a stadium located in the Bronx in New York City. It was the home ballpark of the New York Yankees, one of the city’s Major League Baseball franchises, from 1923 to 2008, except for 1974–1975 when the stadium was renovated. It hosted 6,581 Yankees regular season home games during its 85-year history. It was also the home of the New York Giants National Football League (NFL) team from 1956 through September 1973. The stadium’s nickname, “The House That Ruth Built”, is derived from Babe Ruth, the baseball superstar whose prime years coincided with the stadium’s opening and the beginning of the Yankees’ winning history. It has often been referred to as “The Cathedral of Baseball”.
       
Google Groups: alt.sports.baseball.ny-yankees
Yankees Repeat? Yeah..right!
Frank J. Marasco
Jun 20, 1997, 3:00:00 AM
(...) 
The Yankees are the most recognized sports franchise in the world. They have doubled the championship output of every other Major league team. They have had some of the most storied players in the history of baseball. Arriving to the ballpark for the start of the World Series, John Smoltz said Yankee stadium is a cathedral to baseball. The stadium has also been called baseball’s home office.
     
Google Groups: alt.sports.baseball.ny-yankees
Yanks must stay in the Bronx
Constance Felice
Jul 10, 1998, 3:00:00 AM
(...)
Don’t compare the Yanks with any other franchise, they are in a different league. As they say, the Bronx is the home office of baseball.
     
Newspapers.com
10 October 2000, The Spokesman-Review (Spokane, WA), “Oh, the irony of it all” by Larry Stone (Seattle Times), pg. C3, col. 2:
As the Mariners prepare for their ACLS home opener tonight against the Yankees in baseball’s home office, Yankee Stadium, the omens seem much more favorable.
 
Google Groups: alt.sports.baseball.ny-yankees
New York Wins the WORLD SERIES!!!
Chris Hill
Oct 18, 2000, 3:00:00 AM
It is just a matter of where the trophy is going to be kept. Either in the home office of Baseball, Yankee Stadium, or that big toilet bowl in Flushing.
 
Newspapers.com
21 October 2000, Poughkeepsie (NY) Journal, “Pitiful Mets don’t have a chance to win” by John Ferro, pg. 7C, col. 6:
Yankee Stadium is the “House that Ruth Built”, the “Home Office of Baseball.”
   
Google Groups: alt.sports.baseball.ny-yankees
Bob Sheppard
Flicklives
Apr 7, 2001, 11:44:51 PM
I saw an interview with Sheppard recently, and he doesn’t mind taking a day or two off, now and again. The man is at least 80, if not older, and has been at the mike at the Home Office of Baseball since the late 40’s. He is entitled to some time off.
 
Google Groups: alt.culture.ny-upstate
Do Upstaters root for Yankees?
Bill
Oct 20, 2003, 4:20:50 PM
About once a year, I take my family down to a game at what I consider to be the Home Office of Baseball, or the Baseball Cathedral, or the House that Ruth Built, or, if you prefer, Yankee Stadium.
     
Google Groups: alt.sports.baseball.ny-yankees
A missive to Red Sox Fans and other Yankee haters.
Don Cooper
Oct 26, 2003, 1:44:59 AM
(...)
“Yankee Stadium - Baseball’s Home Office”
 
Twitter
sean_okeefe
@sean_okeefe
Here we go. Game three. Home office of baseball. Greatest City in the World!! Yankees and Twins from the Bronx, Yankee Stadium. Now.
8:34 PM · Oct 9, 2010
 
Twitter
Peelon Musk
@mmigliore
Michael Kay just referred to the Bronx as the home office of baseball. Baseball season is back! #goredsox
1:03 PM · Mar 31, 2011
 
Twitter
Jeffrey P
@JeffreyNYC
Headed for the home office of baseball in the south Bronx… Yankee Stadium
5:54 PM · Sep 2, 2011
       
Twitter
Tom Rock
@TomRock_Newsday
Baseball’s home office: Yankee Stadium.
Quote Tweet
Neil Best
@sportswatch
·
Oct 6, 2015
Commish Rob Manfred to @NewsdaySports on playoffs returning to Bronx: “It’s good to be back here for the postseason” http://newsday.com/sports/baseball/yankees/rob-manfred-it-s-good-to-be-back-at-yankee-stadium-for-the-postseason-1.10930440
7:19 PM · Oct 6, 2015
 
Twitter
GaryAltmanPhoto
@GaryAltmanPhoto
Baseball’s Home Office, Yankee Stadium!! @ Yankee Stadium https://instagram.com/p/BIBgCRJAQGf/
8:46 PM · Jul 18, 2016
   
Google Books
New York Yankees Fans’ Bucket List
By Mark Feinsand
Chicago, IL: Triumph Books
2017
Pg. ?:
Thurman Munson was the heart of the Yankees, a starstudded team that had won two consecutive World Series in 1977–78 to reestablish the Bronx as the home office of baseball.
 
Twitter
Bob Brittain
@WegCook
Replying to @CoachSantella
The home office of baseball. 161st and River Avenue in the Bronx
12:21 PM · Jun 20, 2018
 
Twitter
JDM3
@JDM3_
Replying to @ImMissAdorable
At the Home Office of Baseball aka Yankee Stadium in the Boogey Down BX
He also says if anyone takes a knee he’s “gone” so:
Donny McGoo - don’t bother getting on the plane.  We don’t want you in NY.
No person; man or woman wants a camera to put you on TV in NYC
9:14 AM · Jul 24, 2020
 
Twitter
Jeffrey S. Putman, Ed.D.
@DrJeffreyP
A beautiful but chilly day at the home office of baseball…. and my @YankeeStadium
record goes to 4-0 in 2022 and I get my 90th win… 90-36 lifetime. Let’s go @Yankees! Returning tomorrow hoping to see #61! #RepBX
New York Yankees and Yankee Stadium
1:06 AM · Sep 24, 2022 from Queens, NY