In the sentence "The doctor phoned the nurse because she was late," there is ambiguity about who "she" refers to. Grammatically, "she" could refer to either the doctor or the nurse, assuming both are female.

However, the most natural interpretation is that **the nurse was late**. This is because:

1. The nurse is the more recent noun mentioned before the pronoun "she"
2. It provides a logical reason for the phone call - the doctor calling to check on the nurse's lateness makes contextual sense

But without additional context, both interpretations are technically possible. This is a classic example of pronoun ambiguity in English.
