This sentence is ambiguous — "she" could refer to either **the doctor** or **the nurse**, depending on context. Here are both possible continuations:

1. **"She" = the nurse:**
 "The doctor phoned the nurse because she was late — her shift had started 30 minutes ago, and the patients were waiting."

2. **"She" = the doctor:**
 "The doctor phoned the nurse because she was late — she was stuck in traffic and needed the nurse to start prepping the patient without her."

Without additional context, either interpretation is grammatically valid.
