I've had the flu and a bad cough for a few days. Today when I cough up phlem there is a small amout of blood. What would l have irritated?

Probably not serious. Are you otherwise healthy? Was the blood pink or dark in colour? Are you better from the flu in every other way?
The blood could come from the oropharynx or the lung.
If you are unwell or if the symptoms persist you should see a doctor to evaluate you in detail.

Related Questions

Is this the flu or a cold. No fever. Congestion productive cough but with small amount of blood in phlegm. I have a sore throat and neck hurts.

Could be either. Symptoms of flu and routine viral respiratory disease overlap. If it is within the first couple days then get viral cultures for flu and start tamiflu (oseltamivir) if positive to shorten and decrease illness. Otherwise treat symptoms. Read more...
A cold. Most influenza illnesses are associated with fairly sudden onset of muscle aches, chills and fever, and many feel very ill. Most colds are more gradual onset, without fever, but with the symptoms you describe. You may have a viral bronchitis, which is NOT treated with With antibiotics ,which do not treat viruses. Read more...