Lactogen Cause Phlegm

Hi mummies. My LO is currently 9mths (borned premature corrected age 7mths). He’s currently on lactogen formula and seems to have phlegm. I send him to infant care, he have been having runny nose and cough on & off. Went to see GP and was told phlegm is now infectious. I have friends who told me their LO have phlegm after taking lactogen but GP said milk does not have anything related. Any mummies experience this?