Why is there no direct phone line so that I can call a store to ask a question about a product being in stock in the store?

The stores generally run with just enough staff to stock and check customers out. There isn't someone available to answer the phone so they don't list the phone numbers of the individual stores. Saves them time and keeps costs down because they don't have to pay extra people to field phone calls.

Google aldi's that will give you a corporate number . they can tell you if ALDI'S carriers that product