The correct answer is: C. is phoning/has phoned
The first blank should be filled with the present continuous tense because the action is happening right now. The second blank should be filled with the present perfect tense because the action has been completed before now.
Option A is incorrect because the simple present tense is used to talk about habitual actions or actions that happen regularly. In this case, Bill is not calling his girlfriend regularly, he is calling her right now.
Option B is incorrect because the present perfect tense is used to talk about actions that have been completed before now. In this case, Bill has not finished calling his girlfriend yet, he is still in the middle of calling her.
Option D is incorrect because the simple future tense is used to talk about actions that will happen in the future. In this case, Bill has already started calling his girlfriend, so he is not going to call her in the future.
I hope this explanation is helpful!