VBA Open Cell Reference using Find on text in Column and Row

The ShowDetail method requires Range("I" & Pfind.Row) to be in a pivot table. Your code obscures the nature of this sheet, first by using the Sheet object (which could be any kind of sheet, including a pivot table) instead of Worksheet, then by not specifying any sheet on which to find Range("I" & Pfind.Row) (which means VBA will assume the ActiveSheet) and, finally, by constantly changing the ActiveSheet in your code. Last, not least, your sample workbook doesn't contain any of the "Sheets" the code renames. 

Note that you can access any sheet with VBA without selecting it. Activate and Select are needed for the user interface only. VBA doesn't need either.

I have commented your code and partially re-written it, guessing at its purpose. You now have a function called GetSheet which returns a worksheet by a given name. If the sheet doesn't exist it is created. There is also a function called FindRow. It takes a search criterium and a range as parameters. If the criterium isn't found in the range the returned row number is zero. If the function returns zero no action is taken. Basically, you just need to call these two functions again and again to replace you existing code. That is simpler and therefore avoids the kind of errors your present code contains.

Sub Open_OPEN_PHS_TOTAL()
    ' 02 Jun 2019

    Dim Master As Worksheet
    Dim Ws As Worksheet
    Dim R As Long

    Set Master = Worksheets("Master Report")
    R = FindRow("PHS 3.1 Total", Master.Columns("C:D"))
    If R Then
        Set Ws = GetSheet("3.3 SLA")
        Ws.Cells(R, 8).ShowDetail = True
    End If

'    Dim Pfind As Object
'    Dim Popen As Range
'    Dim TotalSheets As Integer
'    Dim TestSheetNum As Integer
'    Dim TestSheetName As String
'    Dim NewSheet As String
'    Dim SheetFound As Boolean

'    With Sheets("Master Report").Columns("C:D")
'      Set Pfind = .Find(What:="PHS 3.1 Total", _
'                        LookIn:=xlFormulas, _
'                        LookAt:=xlPart, _
'                        SearchOrder:=xlByRows, _
'                        SearchDirection:=xlNext, _
'                        MatchCase:=False, _
'                        SearchFormat:=False)
'    End With
'
'    If Not Pfind Is Nothing Then
'        Range("I" & Pfind.Row).ShowDetail = True       ' which sheet is this range on?
'    Else
'        MsgBox "Not Found"
'    End If
'
'    Sheets("Sheet1").Select                            ' don't select any worksheet!
'    Sheets("Sheet1").Name = "3.1 SLA"
'    Sheets("Master Report").Select
'
'    With Sheets("Master Report").Columns("C:D")
'      Set Pfind = .Find(What:="PHS 3.2 Total", _
'                        LookIn:=xlFormulas, _
'                        LookAt:=xlPart, _
'                        SearchOrder:=xlByRows, _
'                        SearchDirection:=xlNext, _
'                        MatchCase:=False, _
'                        SearchFormat:=False)
'    End With
'
'    If Not Pfind Is Nothing Then
'        Range("I" & Pfind.Row).ShowDetail = True
'    Else
'        MsgBox "Not Found"
'    End If
'
'    Sheets("Sheet2").Select
'    Sheets("Sheet2").Name = "3.2 SLA"
'    Sheets("Master Report").Select
'
'    With Sheets("Master Report").Columns("C:D")
'      Set Pfind = .Find(What:="PHS 3.3 Total", _
'                        LookIn:=xlFormulas, _
'                        LookAt:=xlPart, _
'                        SearchOrder:=xlByRows, _
'                        SearchDirection:=xlNext, _
'                        MatchCase:=False, _
'                        SearchFormat:=False)
'    End With
'
'    If Not Pfind Is Nothing Then
'        Range("I" & Pfind.Row).ShowDetail = True
'    Else
'        MsgBox "Not Found"
'    End If
'
'    Sheets("Sheet3").Select
'    Sheets("Sheet3").Name = "3.3 SLA"
'    Sheets("Master Report").Select
'
'    With Sheets("Master Report").Columns("E:AL")
'      Set Pfind = .Find(What:="Grand Total", _
'                        LookIn:=xlFormulas, _
'                        LookAt:=xlPart, _
'                        SearchOrder:=xlByRows, _
'                        SearchDirection:=xlNext, _
'                        MatchCase:=False, _
'                        SearchFormat:=False)
    ' missing End With

'    With Sheets("Master Report").Columns("E:AL")
'
'    Set Popen = .Find(What:="QUESTION", LookIn:=xlFormulas, LookAt _
'            :=xlPart, SearchOrder:=xlByColumns, SearchDirection:=xlNext, MatchCase:= _
'            False, SearchFormat:=False)
'    End With
'
'    If Not Pfind Is Nothing Then
'        '''''Problem Area
'        Range("Popen" & Pfind.Row).ShowDetail = True
'    Else
'        MsgBox "Not Found"
'    End If
'
'    Sheets("Sheet4").Select
'    Sheets("Sheet4").Name = "Question Que"
End Sub

Private Function FindRow(FindWhat As Variant, _
                         Rng As Range) As Long
    Dim Fnd As Range

    Set Fnd = Rng.Find(What:=FindWhat, _
                       LookIn:=xlFormulas, _
                       LookAt:=xlPart, _
                       SearchOrder:=xlByRows, _
                       SearchDirection:=xlNext, _
                       MatchCase:=False, _
                       SearchFormat:=False)

    If Fnd Is Nothing Then
        MsgBox "Not Found"
    Else
        FindRow = Fnd.Row
    End If
End Function

Private Function GetSheet(ByVal SheetName As String) As Worksheet
    ' 02 Jun 2019

    Dim Ws As Worksheet

    Set Ws = ActiveSheet                    ' remember the ActiveSheet
    Application.ScreenUpdating = False
    On Error Resume Next
    Set GetSheet = Worksheets(SheetName)    ' error if sheet doesn't exist
    If Err Then
        ' create the sheet
        Set GetSheet = Worksheets.Add(After:=Worksheets(Worksheets.Count))
        ActiveSheet.Name = SheetName
        Ws.Activate                         ' re-activate the original ActiveSheet
    End If
    Application.ScreenUpdating = True
End Function

Regrettably, my code doesn't directly address your question. It isn't possible to do that based on the workbook information your have provided. I hope that by replacing your repetitive code with function calls the problem might disappear by itself.