How do I setFocus on a field

When the user clicks a "new" button, our dynamic xds form creates a new row for them to enter data on.  By default the first field (after a button) gets focus.  What we would like to do is have the third field get the focus.

I'm assuming that in the "new" button I would do a setFocus on something.  But as a newbie, I wouldn't put money on that.

I think what is missing is the index of the row.  W/O that, it looks like this:

xfa.host.setFocus(data.sfPage.sfParent.sfTableRow.phone)

TIA,

Jerry