My girls, my nerves are giving out?

My girls, my nerves are giving out ? This is the first time I've encountered coughing with phlegm, it's like a child choking on snot and phlegm, and he's turning blue from all of that! He's trying to cough it up under the night... I've called an ambulance twice now because of fear ? How do you help expel phlegm? How can I help the child?