Sort of like this?
For Each pCell In Range("C2:C" & Range("B" & Rows.Count).End(3)(1).Row)
    If InStr(1, pCell.Value, "TSC") <> 0 Or _
       InStr(1, pCell.Value, "MOBILE") <> 0 Or _
       InStr(1, pCell.Value, "410WED") <> 0 Then

'   "return the entire contents of pCell" whatever that means, and however you do it;)

    ELSE                                       '   !!!!        
    Select Case Len(pCell)           
          Case Is = 6
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],3)"
           Case Is = 7
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],4)"
           Case Is = 8
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],5)"
           Case Is = 9
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],6)"
           Case Is = 10
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],7)"
           Case Is = 11
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],8)"
           Case Is = 12
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],9)"
           Case Is = 13
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],10)"
           Case Is = 14
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],8)"
           Case Is = 15
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],9)"
           Case Is = 16
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],10)"
           Case Is = 17
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],11)"
           Case Is = 20
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],11)"
           Case Is = 21
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],15)"
           Case Is = 32
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],6)"
           Case Is = 42
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],6)"
           Case Is = 43
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],6)"
           Case Is = 44
               Range("D" & pCell.Row).FormulaR1C1 = "= LEFT(RC[-1],6)"
        End Select
    End If
Next pCell

LR = Range("B1").End(xlDown).Offset(1, 0).Row
Range("D2:D" & LR).Value = Range("D2:D" & LR).Value
I think the issue all along has been When to do something, much more than What to do!

I hope that waters are less turbid, now!

Tony