You ask to highlight the rows but I'm guessing this may be problematic (although you don't describe why you want this). Assuming you have 10 rows, and many of those match other rows, your worksheet will look like

The issue is you have no idea which row matches what row!
You will also have the issue when you next run the script, the highlight will persist.
As such, I offer a solution with an extra column of information (screen shot below):
Sub WalkThePlank()
Dim startRow As Integer
startRow = 2 'Update this to lead us to the treasure
Dim row As Integer
row = startRow
Do While (Range("A" & row).Value <> "")
Dim innerRow As Integer
innerRow = row + 1
Dim name As String
Dim task As String
Dim phone As String
name = Range("A" & row).Value
task = Range("B" & row).Value
phone = Range("C" & row).Value
Do While (Range("A" & innerRow).Value <> "")
If (Range("A" & innerRow).Value = name And Range("B" & innerRow).Value = task And Range("C" & innerRow).Value = phone) Then
Range("D" & row).Value = Range("D" & row).Value & innerRow & ", "
Range("D" & innerRow).Value = Range("D" & innerRow).Value & row & ", "
'Rows(row).Interior.ColorIndex = 6 'UNCOMMENT THIS LINE IF YOU WANT HIGHLIGHTING
'Rows(innerRow).Interior.ColorIndex = 6 'UNCOMMENT THIS LINE IF YOU WANT HIGHLIGHTING
End If
innerRow = innerRow + 1
Loop
row = row + 1
Loop
End Sub
This is what it does

Do this on a copy of your file - there is no undo feature!
Note in the code there are 2 lines showing you which line to uncomment (remove the first ' on those lines and they will highlight)
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