The issue of work related phone use is a complex one, the original legislation banning use of a handheld mobile phone whilst driving has by and large proved ineffective, even after the original legislation was given teeth by the ability to add penalty points upon conviction. The legislation in my view is unlikely to significantly reduce drivers using handheld mobile phones, unless the police take positive and active steps to prosecute drivers caught using a handheld phone whilst driving.
The police have always held the view, supported by a number of academic studies, that usage of a phone while driving regardless of whether handheld or hands-free, will result in a distraction to the driver. It is for this reason that the police will routinely seize mobile phones and will investigate phone records, in cases where there has been a fatality or life changing injury as a result of a road traffic accident where use of a phone is a suspected contributory factor.
The involvement of work related calls does put a different slant on the issue, if the police can demonstrate that a driver was taking or receiving a work related call there is a possible prosecution against the employer for aiding and abetting the offence. If phone use is suspected after a serious accident, the police will check to see whether the employer had a policy in place governing use of a phone whilst driving, further was the employer complying with its own policy and monitoring phone usage. This approach is enshrined in the ACPO Investigation of Road Death Manual.