Dropped a phone on my nose 4 months post rhinoplasty, should I be concerned?

Thank you for your question. It depends on how you feel after the contact. Bruising, swelling and bleeding would be more concerning. Please feel free to discuss your recovery with your board certified facial plastic surgeon to ensure that you are on the right track.
Best wishes,

Thank you for the question. At four months post-op, it is not likely that a mild trauma will cause any major or lasting changes. Some swelling may occur, and you can manage this with ice and head elevation. If you see any structural issues, please visit with your surgeon for an evaluation. Take care.

It takes a lot of force to break the nose, and simple dropping a cell phone does not have enough force behind it to fracture nasal bones or cartilage.

At 4 months a lot of the healing would be done. And it also depends on the degree of trauma. From what you are describing, it seems the impact was not too strong. As long there is no pain, bleeding or significant swelling,  you could wait and see. If you have ongoing concerns, please see your surgeon, as proper advice can only be given after a physical examination.

Your nose has healed, however you can always re fracture your nose. A ct scan might be recommended is you are concerned. 
Sincerely
GD