Source?
Not true as far I can tell. I don’t see Philosophy as a dominant course of study at the doctoral level. Science and math are at the top, for example:
OECD Report 2019
“…The broad field of natural sciences, mathematics and statistics attracts the largest share of doctoral graduates, 23% on average across OECD countries, followed by engineering, manufacturing and construction, and health and welfare, both at 17% (Table B7.2). In contrast, business, administration and law, which accounted for the largest share of graduates at bachelor’s level, represents less than 10% at doctoral level…”