The correct option is
C Hadn't phoned
NOTE: Looking at the sentence, we can understand that there are two actions. 'Mrs. Kapoor was worried' because an action happened in the past. Hence, we will use the past perfect tense to fill in the blank.
Option A - 'Hasn't phoned' is used to represent the sentence in the present perfect tense. Thus option A is incorrect.
Option B - 'Wasn't phoning' is used to represent the sentence in the past continuous tense, to explain an action that was continuing in the past. Hence, option B is incorrect.
Option D - 'Didn't phones' is grammatically incorrect as even in simple past tense, we don't use the verb with 's/es'. Hence, option D is incorrect
Option C - 'Hadn't phoned' is used to represent an action that was completed in the past before 'Mrs. Kapoor was worried'. Thus, it defines the sentence in the past perfect tense. Hence, option C is the correct answer.
'Mrs. Kapoor was worried because her husband hadn't phoned.'