No sound after zoom screen is minimized on iPhone

I hosted a zoom meeting from my windows laptop this morning. One of my clients told me afterwards that she couldn't hear the sound after she minimized the zoom screen on her mobile phone. But this won't happen if she joins other people's zoom meetings.

I did the test myself by joining my hosted meeting from my iPhone. After I minimized the zoom screen on my iPhone, I couldn't hear the sound as well. When I joined the zoom meetings hosted by other people, I can still hear the sound after the zoom screen is minimized on my iPhone. So I think this must be related to meeting host settings. Any solutions?