Ah chest colds. Yes my DS had a rather bad chest infection when he was 1 (a week in hospital with various treatments).
Since then pretty well any cold he gets goes straight to his chest.
I'm happy to live in a rather anti- antibiotic part of the world but we have had to use them a few times with DS, not much ill effects only decreased appetite for a while afterwards and sometimes a bit of an upset tummy, probiotics have generally helped and no ill-effects lasting more than a week or so after the antibiotic course finished.

Re beating it off without antibiotics: We've found raising the head of his bed really helps him to breathe better while sleeping and then clear it out on his own. You can do this either by putting a blanket under the head of the mattress or putting something under the bed legs at the head of the bed. Vaporub can help a little. Actually I think moist air with a bit of eucalyptus or vaporub helps them to get the phlegm out. I think the moist air helps open the airways in the lungs. Our DS only had trouble once he was old enough to communicate more with so we also encouraged him to cough to bring it up. You can also do a bit of chest percussion, you lay them on your lap with their head below their body and hit them on the back (lightly but firmly) with a cupped hand. It should make a good sound but you obviously don't want to hurt them. The idea is to vibrate the air in the lungs to move the mucus from the small airways to the larger ones where they can cough it up better. You start at the bottom of the lungs and move up if I remember rightly. Also look into postural drainage positions for children. I've always just done it with the head lower than the body but I just saw there are a few different positions which drain different parts of the lungs better. Apparently it's better to do the postural drainage and percussion together after time with the vaporizer.

Good luck! I hope your DS recovers quickly and doesn't need the antibiotics.