If you're asking the question (how can I sell my old phone online?) then, well you've came to the right place. You have a few different options, and I'll do my best to explain the benefits of them all.
Online auction. This might just be the most popular option out there. It's no secret eBay is the leader in this market, it's a great option but there are a few drawbacks. To start with the amount of potential buyers is nearly endless, which is about the only positive. This is the option that may net you the amount of money for your old smartphone, but you do have expenses involved. First of all, you are going to need a paypal account to receive a payment, not to mention how to retrieve it after you receive the money. The biggest hurdle with eBay is dealing with the customer, the 10% selling fee and shipping cost (just my opinion of course.) I have had the worst luck with buyers not paying and dealing with the shipping process. This has been enough to turn me off of the online auctions, as a seller anyways.
Sell to an online whole seller. This is the most "handsfree" system out there, and of course I would say the best hint hint www.buyingphones.net To be fair you may not get as much as you would on eBay, but you will likely make out with more money in the long run (- the fee and shipping expense) To get started you get a quote from the site, and if you agree to the price, you'll be sent a pre-paid shipping label and box to send the phone to the sellers. After the phone is received it is then inspected and then you will receive payment within the next 24hr. That's it.
Social Media/ classified website. This has many of the same effects as the online auction, as far as endless buyers, but it has it's own set of drawbacks. You will get pretty good money this way, but you do have to deal with the customer yet again. The main problem I have had with this method is getting the buyer to appear at the agreed time and meeting place...really this can be a difficult task!
Any method you choose make sure to always delete your personal information! You also need to make sure you disconnect your apple id, google cloud, email etc so the phone can be used by another person. Always do a factory reset, maybe twice, yea do two resets before the phone leaves your hands!