Get their attention
Having a person’s attention would mean ensuring that they are listening and understanding the words you say. In a face-to-face meeting, this would mean making eye contact and checking in to see that they are listening. In a call however, this can be a different ball game.
This is worse when considering possibilities such as the other person being distracted or in the middle of doing something else while on the phone. The right communication tools such as MultiCall however, can help with this.
Using your visual display of Call Monitoring, check who’s on the call and direct your questions to someone new every time in order to make sure that everyone is involved, and not multitasking.
If they seem distracted by something, ask for their attention, or confirm that they are okay and that they understood whatever was mentioned. Note however, that this does not mean calling them out or yelling at them. Belittling someone publicly can also risk poor team communication since they could fear to speak up another time.