I Need to boost a public Wi-Fi Signal?

I work in a building that has public Wi-Fi, and I'm trying to use it to play iTunes Match on my iPhone at my desk. My phone picks up the network, but the signal is not strong enough for Match to work. I've been looking around at repeaters, but everything I see requires physical access to the router for setup. I do not have access to the router in my building. I'm at my desk all day, so a physical connection between a high gain antenna & my phone would work if that exists. My phone is a 5S, so it has the Lightning connector.

You can use range extender to boost your signal.

You just have to face reality that you won't be able to do this at your desk.