Welcome in H.C.M.
After reading your query I came to knew that you are smoker and taking alcohol and suddenly you developed pain in left side of throat, in the same time you noticed blood in phlegm.
Since you are having pain in left side of throat therefore local inflammation is suspected in throat and most likely blood had came out from this site probably.
Keeping all these things in mind you may do-
1- Culture and sensitivity of throat swab.
3- blood- CBC, ESR
, Prothrombin time
, blood sugar (F & PP).
In this way we may reach to possible cause for your symptoms, but examination by ENT specialist
is appears to be necessary here to rule out any local pathology in throat.