The following methods worked for me:
1. Vicks Vaporub for infants
2. Dehumidifier in the room
3. Before sleeping, bring baby into a hot steamy shower so the moisture can ease the phlegm
4. Sleep on an elevated wedge, or put a rolled towel below baby mattress, or tummy down (my baby slps tummy down)
And of course, more breastmilk means more antibodies and a faster recovery. I would offer more feeds as well to hydrate baby.
Anrevify