Dot convention meaning
Reality is this - if you apply a voltage source to the primary of a transformer then the phase difference between primary voltage (dot end) and secondary voltage (dot end) is zero. In other words the dots tell you about the phase relationship between primary wires and secondary wires.

Because of this, if you have a load resistor connected to the secondary, load current flowing into the dotted primary wire is matched by a secondary current flowing out of its dotted secondary wire. This of course is a 180 degrees shift.

The above analysis ignores magnetization current.