Currently within the Portfolio view, you are unable to Filter by Number or Text field types. You are, however, able to Sort by them. This is an unnecessary limitation. Allow for being able to select these fields in the Filter dropdown of the Portfolio view.
Just for context, you cannot use text or number fields to filter tasks in projects either. 
Just curious, why just portfolio List views?
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Within Project View, you can Sort by Numbers/Text, but not filter.
Within Portfolio View, you can neither Sort nor Filter by Numbers/Text.
Thanks @Richard_Sather, I didnt catch the limitation of being unable to Filter within projects. I think it makes sense to have the ability to Sort/Filter by Text/Numbers in both projects and portfolios.