If you haven't updated iOS to the latest version, which for your device is iOS 12, I'd recommend installing it as it's really a great update (I use it on my 5s 🙂
About the link, once you copy it the link will be in the clipboard of the phone and you can go ahead and paste it wherever you want on the phone or you can use one the short ways to share your playlist or a single song offered when you use the Spotify's share interface or you can use the iOS ones.
Hope it helps 🙂
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