How do you get all the air bubbles out of a concrete pillar?

Air bubbles are not always a bad thing. Sometimes air is entrained purposefully to achieve certain material properties. You obviously do not want any large pockets as those would be stress concentrations. Concrete mixes are sometimes vibrated to get the mix to settle and get the air out and prevent aggregates from clumping. Some mixes if they are thicker are more workable than others and are not as prone to creating air pockets.

Vibrating the wet mix and pouring slowly and carefully are the best ways.

I don’t know much about concrete, but my guess would be suck, don’t blow.

Yep, Industrial strength vibrators applied to outside of the form as the wet mix is poured. And don’t lean up against the vibrator lest you release a bit of wet mix of your own. :-)

The most popular cylindrical forms are Sonotubes. They are usually vibrated during the pour. If you want voids you insert them.
You can buy the tubes and voids from the site above.

This is not the question I expected to run into the term Industrial Strength Vibrators.

If the pillar is not too deep and you are pouring by hand, you can achieve the same by using a long 2×4 or a long piece of pipe. Insert it into the form from the top and move it around so any unintended voids can work their way to the top as air bubbles. It is pretty labor intensive. The industrial strength vibrator (not that one, this one!) would be a lot faster. You might try a local equipment rental place to see about rental rates.