Depending on how much of the steps are damaged, based on the fact that it's turning into powder most tradespeople will want to replace the whole front steps. The powdering might mean that the concrete never was mixed properly in the first place. However if you want it patched, most handipeople will be able to do the job. You also might want to do it yourself; I had some front brick steps that needed patching and one small bag of quickrete (home depot) did the job. Beware: quickrete does set up quickly! I lost a bucket because I wasn't fast enough.