HiCustomer


It is possible your dog may have caught an upper respiratory illness such as kennel cough or possibly canine influenza. A heart condition such as heartworms can also cause a cough, which will need to be checked if your dog is not on heartworm preventative or an older dog.   

Kennel cough is normally contracted when a dog has been boarded or kenneled or around a large number of dogs such as at a dog show, dog park or pet store. Here is a website with more information on kennel cough. http://www.thepetcenter.com/gen/kenc.html

Canine influenza is now becoming more prevalent and like it sounds it is a canine flu. Here is an excellent site on it.    
http://www.cvm.uiuc.edu/petcolumns/showarticle.cfm?id=475

You will want to monitor your dogs condition looking for colored discharge from the nose or eyes, a productive cough (coughs stuff up), stops eating or lethargy. These are signs of a possible bacterial infection as well and my require antibiotics. If your dog appears to be having a difficult time breathing, you will need to see your Vet as some dogs dog get really sick with canine influenza and need support to recover.

To help your dog breathe easier, Robitussin DM at a 1/4 teaspoon per 5 pounds can be used to control the cough. Dosages can be obtained at this website. http://www.petplace.com/drug-library/dextromethorphan-robitussin-dm/page1.aspx

The following site goes over the canine cough.
http://www.canismajor.com/dog/cough.html

Since your dog is an older dog and she is coughing up phlegm, I would have her seen by your Vet rather than wait for the symptoms to worsen.

I hope you find this information helpful.
Coughs