I need to clarify which interpretation you'd like me to continue, as the sentence is ambiguous. The pronoun "she" could refer to either the doctor or the nurse:

**If "she" refers to the nurse:**
"The doctor phoned the nurse because she was late for her shift and hadn't notified anyone about the delay."

**If "she" refers to the doctor:**
"The doctor phoned the nurse because she was late for rounds and needed the nurse to start checking on patients without her."

Which interpretation would you like me to expand on?
