people can't hear music or host talking

I am having issues with participants being able to hear the music and voice of the host?  We have never had this problem until 3 weeks ago.  I have deleted the zoom app, reinstalled it, powered off the iphone and have looked through all of the settings to figure out what is wrong.  We purchased 2 brand new iphones to not have any more zoom issues to keep our members happy.  This is a major issue and needs to be resolved.  How can you help?