Some of the herbal teas called Throat Coat or similar are pretty good for a sore throat, especially with a generous spoonful of honey.
Hot honey and lemon juice is good, too. Basically a hot lemonade, but not the sugary stuff from the stores. Squeeze a fresh lemon into the cup, a spoonful of honey and top it up with hot water.
The other ideas from above, designed to loosen the phlegm and make it easier to cough up are good, too.