Take a text string and parse out and result in defined abbrevations

Try this:

Function Abbreviate(ByVal sInput As String)
    Dim vList() As Variant
    Dim l As Long
    
    With Sheet2
        vList = .Range("A2", .Cells(Rows.Count, 2).End(xlUp))
        For l = LBound(vList) To UBound(vList)
            sInput = Replace(UCase(sInput), vList(l, 1), vList(l, 2))
        Next l
    End With
    Abbreviate = Replace(Trim(sInput), " ", "_")
End Function

Use as a worksheet function - in Sheet1!B2, enter:

Formula:

=Abbreviate(A2)