I'm in Canada so not covered by the same laws as US states, but a few years back i went to my gp with what he quickly diagnosed as a life-threatening blood clot. He explicitly stated "i don't think we need to call an ambulance but you need to go to ER immediately". He gave me a note for the triage nurse to expedite admitting and i was into the ICU within the hour.

My wife drive me by nothing stopped me from using a taxi or ride share.

Doctors definitely have a duty of care that must consider emergency transport, but it's be surprised if laws explicitly stated you need to call an ambulance for stable patients that need emergency treatment.