Gagging and choking on nothing

Hayleigh

My sons 8 months and for the last month hes been randomly choking or gagging on nothing its like hes got something stuck in his throat but i know hes not eaten anything he shouldnt have. This morning hes had a bottle and started doing it after about 30 minutes hes then sicked up 3x with quite a bit of phlegm in it is this normal? He always looks like hes chewing on something