Add New Row Loop?

I use the following code to add a row to an existing table

Dim newLineRow As DataRow = dsAccountDetails.Tables("Ph").NewRow()
newLineRow("Service TN") = "test"
dsAccountDetails.Tables("Ph").Rows.Add(newLineRow)

When I run the code it adds a single row to my table just like I want it to. However, when I put it in a loop it errors and tells me that the row already exists. The number of rows is always changing and I want to build the table from arrays. Why isn't the following working?

Dim a As Integer = 0
Dim b as integer= 5
For a = 0 to b
dsAccountDetails.Tables("Ph").Rows.Add(newLineRow)
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