If you don't want to be disturbed leave your phone on silent or don't answer it.
As far as i'm aware there is no requirement to be contactable on a D/O or outside the the hours of a standby duty. Your D/O is supposed to be a period of rest free of duties so its entirely up to you whether you choose to speak to 'work' or not. Personally I tend not to answer the phone on a D/O but if they leave a message and its important i'll call them back as long as it doesn't compromise my personal plans.
