You may wish to check successful selling prices for your phone on ebay to get a fair idea of what your phone is worth and how well they are selling. Swappa is another place to check to get a fair idea of value.
I'd go with swappa over ebay. You're selling through a site that holds people responsible for selling working phones that match their description, which means if you are actually selling a phone in good shape you should be able to command a lot more money for your phone.
You've probably seen this already but there is a $200 promo from Sammy for the Note 4 until July 26th. You may want to buy asap and hope to sell your phone after the promo.