There is a lot of guessing what exactly your ISP is providing. E.g., are you actually connecting to your ISP via Wifi? Or via ethernet? In either case, since you are assigned a specific IP (a public IP? or private? Do you need us to tell you what a private IP looks like?), repeating is not going to work. You will need to route instead.
Since you get only one IP (according to my guess), you can connect only one device directly to the ISP. Presumably, you want to connect your MT300N to the ISP (preferably via ethernet) and connect both your PC and your smartphone to your MT300N via Wifi.
But I am only guessing. Maybe you are assigned several IPs by your ISP? How many?