The sentence is **grammatically ambiguous**, meaning it does not explicitly state who was late. 

*   **Interpretation A:** "He" refers to the doctor (the doctor was late, so he called the nurse to inform them).
*   **Interpretation B:** "He" refers to the nurse (if the nurse is male, the doctor might be calling to ask why the nurse is late).

Because "he" could refer to either the subject ("doctor") or the object ("nurse"), there is no way to know for certain who was late based on the grammar alone. This is a classic example of a **Winograd Schema**, where the reader must rely on context or real-world knowledge to resolve the pronoun; however, in this specific sentence, the context remains unclear.
