I have an S7 myself. Does your service provider permit your phone to act as a wifi hotspot? If so, you can turn this on and have your Roku connect to the network name (SSID) and password used by your hotspot.
I do have home internet, but I've swithched my Roku over to my Verizon-connected phone hotspot a couple of times when my normal internet was down.
- Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
- Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T
- TCL Roku TV 43S425/C107X, Ser X000001R60KV, wifi