It is clear from the question that the answer must be an adverb that modifies the verb 'telephoned'. Also, the sentence has a negative tone and it must not be changed. Hence, the adverb must be positive since two negatives make a positive. Further, the sentence indicates that the action is incomplete at this time and the answer must justify that.
Option A is incorrect. When 'yet' is used in the middle of a sentence, it indicates a condition and not time. Also, as per the rules of usage, yet must be located between the auxiliary and the main verb when used in the middle of a sentence. Thus, it will make the sentence grammatically incorrect.Option B is correct. 'Still' is an adverb that indicates time. It is also a positive adverb and so, does not change the tone of the sentence. It justifies the action being incomplete at this time. Thus, it meets all the required conditions.
Option C is incorrect. 'always' is an adverb that indicates time but it does not justify an incomplete action. the word 'always' suggests a long period of time while in the given context the situation is about the current instance.
Option D is incorrect. 'never' is an adverb but it does not justify or indicate that the given action is incomplete. Further, never would make the sentence positive as two negatives make a positive sentence.