Difficult to assess severity on phone without examination of chest. Simple nasal block with mucus can easily treated with Normal Saline Nasal drops ( Nasoclear nasal drops 1 drop each nostril every 4 to 6 hourly before feeds)
Next Steps
Maintain pleasent room temperature, Avoid air turbulence ( high speed fan) near nose to decrease mucus production.
Health Tips
In case of no improvement get pediatric pulmonologist opinion to rule out soft larynx ie laryngomalacia or other causes of congenital stridor