Phlegm, Cough, Throat Infec, couldn't

My father is 68 year old. From last 15 days he is having sore throat, not able to speak properly, not able to eat and when he drinks anything he is getting cough continuously. Met ENT he has prescribed some medicines but it didnt work and we went to pulmonologist where he mentioned it's a heavy infection in throat and chest. He is doing better compare to last before week but doctor again suggested to meet ENT to do some throat related test to check the infection status. He is very weak and not able to speak with that sore throat. BTW, Blood Test and CT Scan reports were taken and it was showing white patches in the chest area. Doc said it's an infection so will take sometime to clear. I don't like to meet any other doctor unless the given course is completed. Is that okay to go ahead to do that Tests (I think endoscopy)? Or I need to meet any specific doctor to check?