Test blank cell and out put phonetic (text)
Give your code a good name - not test - it doesn't tell me what it's doing. 

At the same time, it's implicitly public so you might as well put that and always turn on Option Explicit. You can have it automatically by going to Tools -> Options in the VBE and checking the Require Variable Declaration option. This way if you have any variables not defined, the compiler will let you know.

You can use Do Until isEmpty but why not find the last cell and use a For loop? There is a standard way to find lastRow and lastColumn. That post explains why.

Technically you could eliminate If Cells(i, 2) &lt;&gt; vbNullString because the lastRow should determine that, but so would your Do Until isEmpty so it's already repetitive. You can also avoid assigning i an initial value and get rid of your messy (for VBA) iteration.

I would also eliminate the if block, personally. 

Option Explicit

Public Sub GetPhonetic()
    Dim lastRow As Long
    lastRow = Cells(Rows.Count, 2).End(xlUp).Row
    Dim i As Long
    For i = 1 To lastRow
        If Cells(i, 6) &lt;&gt; vbNullString Then Cells(i, 6) = Cells(i, 2).Phonetic.Text
    Next i
End Sub


Also eliminate the commented code - if you aren't using it, it's just noise. I also eliminated the extra white space as you don't need it.



Re:


  I am also wondering if there is a way to set the starting point to be
  Column B (therefore, Cells(i,1)=B1) and possibility replace Cells(i,2)
  by dim as something(long?)?


I'm not sure what you mean here, you are already dim i as long and using that to determine your starting point; there's no need for it to be more complicated than cells(i,y).