Hello,
Phantom smell may be due to halitosis(due to infections of the oral cavity or poor hygiene),smell from the sweat or smell due to nasal or sinus infections.As you are also having the symptom of mucus in the nose,so fungal sinusitis also has to be ruled out.It produces a bad odor which you can feel as bad smell.
I sincerely advise you to consult an ENT specialist and get yourself evaluated fro sinusitis.Transillumination tests,ultrasound or CT sinuses and fungal culture of the nsal mucus may be needed.
Hope it helps.Take care and pls do keep me posted on how you are doing and if you have any additional queries.