My 3 years old is down with phlegmy cough. Any remedy to clear the phlegm?

Best to see the doctor

See a doc , alternatively u can try giving freshly squeezed ginger juice with lemon juice and honey. Works well for my kids , u can adjust the taste, kids usually won’t prefer the strong ginger taste so u can add more honey n tangy lemon( not too much ). You can also give water with cumin. Boil water with cumin n let your baby drink it.