The problem is estimated to cost businesses £2bn a year in lost revenue, along with 80 million lost work days. Some 50% of stress-related workplace illness is thought to be caused by bullying.
By signing up to the service, retailers can get HR advice designed for smaller businesses of five to 25 employees.
Co-founder Simon Dawson said: "Telephone mediation is a very efficient way for employers to handle workplace conflicts. In fact, it has even been shown to be more effective at dealing with bullying than face-to-face mediation. Unfortunately, to date, it has not been readily available to managers of smaller business, which is why we are very proud to be introducing this new service."