Transformer's Primary and Secondary Voltages
which is the phase relationship between the primary and secondary
  voltages


The dot convention tells you which terminals will have secondary and primary voltages in phase: -



Above picture from here. Consider also this picture of two identical windings wound the same way: -



For any secondary load current, the primary load current will be 180 degrees out of phase at the dotted terminals. Consider this picture for the current: -



Lower pictures from here. See also this answer for a wordy version of the above.