With only a single team in each professional bb or fb, not so for New York, LA , or Chicago, (only fb), at 1, 2, 3.
Philadelphia lost the A's in '54 and until then the town had been an American league team since before WWI. I don't know anyone over 70, including my parents, and aunts, and uncles, who was a Phillie fan before the A's left town. In fact, the Philadelphia A's won pennants in 1902, 1905, 1910, 1911, 1913, 1914, 1929, 1930,and 1931. The teams of 1910, 1911, 1913, 1929,and 1930, won the World Series. The Athletics could easily be proclaimed "Philadelphia's Most Successful Sports Franchise".
So, the Phillies became Philadelphia's "team" approximately at the same time the Dodgers and Giants became LA's and San Francisco's teams.