What is the French phone number for medical emergencies?

112 is your best bet for life threatening emergency services across the EU. It's the equivalent of the US 911 system, with regional centers that will dispatch the closest applicable first responders to your location.

Fire services in the EU don't generally handle medical emergencies (unless they develop in the line of their regular business or they're on scene when the emergency develops). Same with police.

Calling a hospital would most likely lead to the hospital putting you on hold for triage by the phone hotline of their emergency room, who then will decide whether you should come over, call a non-emergency doctor, or are in need of an ambulance.

In general, that's what you'd do in most of Europe when you are in need of quick medical attention outside of office hours of family doctors/general practitioners and it's not urgent enough to have ambulances and/or other emergency crews rush to the scene with all lights and sirens blazing because every second counts towards saving a life in imminent danger.

Do remember that abuse of the 112 system can be a crime.

The 112 is probably your best bet. It's available across the EU and handles all kinds of emergencies and dispatch the appropriate response teams. French people are more and more encouraged to call this number since it minimizes the risk of "calling the wrong service".

The 18 is also a good bet. As you know, they call the fire-fighters but they handle injured persons as well. For example, if there is a car crash, fire-fighters will dispatch an ambulance of theirs to take care of the injured and bring them to the hospital if necessary.

The 15 is for severe injuries. The SAMU can be dispatched in car crashes for example, but mostly when there are severe injuries.

Since these last 2 numbers are national, it is less likely that you will speak to a person who is skilled in English (prepare for ze Frenche accente).