Due to the earth's obliquity and aphelion shouldn't southern hemisphere be experiencing a colder winter?
It would be, but the southern hemisphere has a large area of water.
The Earth does receive less sunlight in July when it is at aphelion. Curiously the Earth is on average a few degrees warmer at aphelion than it is at perihelion. The reason for this is that the southern hemisphere has large areas of water which retain heat due to water's high specific heat capacity. The northern hemisphere has large land areas which heat up quickly and cool down quickly.
When aphelion occurs in the northern hemisphere winter the northern hemisphere will experience colder winters. Due to apsis precession this will be the case in about 12,000 years.