Star delta phase difference
The easiest way to think about this, is that it comes from the conversion between Y and \$\Delta\$ configuration. 

See this question for the math:

Why does a delta/wye transformer make 30 degrees phase shift ?

To answer your question, converting to \$\Delta\$ gives a leading 30 degree phase shift and converting to Y gives a 30 degree lagging phase shift. Both Y-Y and \$\Delta\$-\$\Delta\$ give no phase shift.

edit: this assumes we keep our abc phase connections in the same order.