First you check consciousness and breathing, so that when you call an ambulance you are ready to answer questions about the victim's condition. Breathing always matters more than immobilizing the leg.
In any medical emergency, once the scene is safe, the first step is to assess the victim's basic vital functions. You must check their consciousness and breathing to find out whether immediate life-saving resuscitation is needed, which comes before treating the leg fracture.
Option 1. You must first check the victim's condition, so that when you call an ambulance you can give the dispatcher accurate information.
Option 3. Checking for life-threatening problems, such as absent breathing, always comes before dealing with local injuries (fractures).