OpenAI is hardly “some random company”. It’s 49% owned by Microsoft, and has an exclusive commercial license with them.

Its cofounders and original investors are all Silicon Valley luminaries, plus Elon Musk who’s since sold his stake. Cofounders and major investors include Sam Altman (former Y Combinator president and now OpenAI CEO), Reid Hoffman (LinkedIn cofounder), Jessica Livingston (Y Combinator), Peter Thiel (Palantir), Amazon Web Services, Infosys, and OpenResearch (formerly YC Research).

Btw I’m not sure if you need a phone number if you sign up with a social media account like Google.