The phone number is only for you. Players never see each other's email or phone.
To change someone, press Open record, make the change and press Save. The record also has an Email button to write just that person.
When someone leaves, open their record and press Take off the roster. They stop getting polls and offers. Past answers are kept. To bring them back later, add them again.
Download as spreadsheet (CSV) gives you name, email, phone, chair and section for everyone. It opens in Excel or Numbers. There is no import from a spreadsheet yet, so add players one at a time.