Hello As you mentioned that there is cough , clear phlegm and impacted ( gag in throat ) and all reports are clear. In my opinion at this age of 73 years , particularly during the time of sleeping such symptoms may be due to bronchoconstriction . As this produces cough ( aggravate during sleep ) , post nasal discharge and gurgling sound with wheezing is the characteristic feature of such bronchoconstriction. When such patient visit I prescribe syrup containing pseudo-ephedrine with terbutalin+ ambroxol ( this is cough syrup and also bronchodilator), However , hot coffee and steam inhalation will also provide relief in such typical situation. In my opinion , since phlegm is clear so no need of any antibiotics. But this is a prescription drug , so consult your treating physician and get his opinion. Good luck.