Edit 'Primary Number' Standard User Field in Taleo/Fluid

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HI Experts, 

We would like to modify the 'Primary Number' Standard User Field in Fluid but I can't find a way to do this in Configuration > Candidate Fields or under File Configuration > User Defined Forms. Currently 'Primary Number' is set up as a drop down with various options, and we would like to remove 'Pager' and 'Fax' from this list. 

The drop down list is not editable in the User Defined Form Field Editor. 

I've attached some screenshots to demonstrate. 

Thank you

Emma