Phlegm in newborns

I have a two week old bby girl. And this morning she was having a hard time breathing due to phlegm. I had to use the bulb syringe to help her. It was scary. I don't know if I should call her pediatrician because what if it was a one time thing...I am concerned though. Or should I wait and see if it happens again? I'm scared though that I might not hear her chocking.