This error message is a programmatic error which does not help to solve the exception.
However it can appear in the following scenario which has been fixed with Importacular 2.9.
The issue is around the way in which phone and emails have been mapped. Specifically the phone type. The setup below is incorrect:
When you look at the mappings the phone type is mapped to the incoming value of "Phone". The incoming value in the "Phone" column will be a telephone number not a phone type. If there were a column that said "phone type" and the value was "Home" or "Mobile" then as long as these values are in the RE phone type code table then there will not be an issue with this.
It is very rare that a third party data source would have the phone type value coming in from their data. Instead that field should be mapped as a default value. This is shown in the screenshot below.