2 points to help you here. There are many ways to handle this differently.
Taking the phone call yourself, you have identified.
Second thing is to actually find the Nurse who talked to the MD and talk to her.
You made a lot of assumptions about what was said on the phone and also about what the other RNs nodding was about.
I'm reading that you relied on a note, and overhearing part of a phone conversation to make some decisions for patient care.
So you can see, in a more critical situation, how well that would go over if you had to explain that to your manager or anyone else.
But what I do not understand is how anyone knew she was dig toxic, if she had no labs.
If she had labs, then you know, you need to do a quick looksie at your patients labs. I know you are busy,but you would have known she was dig toxic, and no matter what else was said or done...you would have been in a much better place to take care of the patient.
If she had no labs whatsoever, then no one knew she was dig toxic, but they may have suspected it. Of course...if you Suspect someone is dig toxic, and they are getting a level to assess for that, you might want to ask or think about "Maybe I should hold the med until the result comes back"
Your unit is hectic and very busy, which makes things challenging, but you have to be assertive. If an MD hangs up, Call them back. It is their JOB, do not let them intimidate you. For a while, you may want to insist on talking to the doctor directly. You can do this. It does get better, and you are going to be much better at managing everything soon. Because you care (which is obvious), you are going to make the effort to get it and you will succeed!