Do not worry,
Temperature monitoring at different site range in different values so proper temperature monitoring required
Yellow phlegm point toward cold cough he is not having dry cough
At the age of 73 immunity decreases so more prone for infection as he is having infection kindly avoid him to go to crowded place upto symptoms resolve
Next Steps
Prescribed medicine may take 2 to 3 days to resolve the symptoms ,trust on doctor is required
Health Tips
steam inhalation with 2 tablespoon of Vicks in hot water may help to resolve symptoms faster ,
Avoid eating refrigerated item upto symptoms resolve
Do not do exaggerated working
If persistent of symptoms/ worsening of symptoms kindly consult to doctor