Connecting with two different Networks

Hi All,
I am having a Broadband connection at my PC (with Static IP) and I have a 4G internet on my Phone.
I am running a server on my PC that's why I took Static IP. My broadband upload speed is 2mbps only, so I want to connect to the internet via 4G Phone through USB Tethering because it has 8mbps upload speed. I did so and I connected 4G phone via USB Tethering mode and I got two networks on PC. But my IP changed to a Public IP assigned by that 4G Network Provider. I want to use that static IP on my PC and also want to use 4G internet speed. I tried Bridging Network, but wen I did so, My IP changed to some Public IP but I was able to Ping the 192.168.1.1 router and the 4G Internet gateway.

In Short : I want to use the Static IP provided by Broadband Provider and the Internet Speed of the other 4G Network simultaneously.

Any workaround you can also suggest like redirecting from router etc.

Thanks in Advance!

This may require professional equipment, please see networking - Can I configure a server to use a different network conection for Upload/Download - Super User.

However, the 4G connection shouldn't affect IP of broadband connection.
Disable bridging and return back to what you had originally.

Now, I wonder if this would work:
- You are connected to both networks
- Configure the gateway metric of 4G to be lower than broadband so 4G is preferred.
- Spoof the IP of 4G with the broadband's static IP (if the PC is getting the static Internet IP and not a private IP from the router)