You can use something like AutomateIt. You can set it to put your phone to silent when the librelink app opens, then go back to loud when the app is closed.
It should do exactly as you want, pretty seamlessly.
Unfortunately not, and as far as I'm aware it isn't going to be any time soon (if at all). I think it has something to do with the NFC capabilities on iPhones being strictly reserved for Apple Pay and not open for use by developers and 3rd party applications.
You can use something like AutomateIt. You can set it to put your phone to silent when the librelink app opens, then go back to loud when the app is closed.
It should do exactly as you want, pretty seamlessly.
It only stays on silent while the app is in the foreground, basically when it's the app your actually using in screen. When you switch to another app it'll revert back to loud (or whatever sound profile you want)