If an adorer's notification preference is Phone call and they are marked as a substitute, they will eventually receive a phone call invitation to claim a substitute request.
However, if they don't answer their phone and don't have voicemail, or if the line is busy and they don't have call waiting, then We Adore Him will postpone that invitation by 2 hours and then try calling again. If that follow-up phone call would be made outside of daytime hours, then it will be postponed until the following morning.
Note: the flow is slightly different if they have voicemail. Learn more.