Static IP WiFi Sharing

If you have one IP address, what you could do is configure both with the same IP address and then make sure that only one device is turned on at the time. By this, put the iPhone into Airplane mode when the MacBook is on. You will also need the subnet and DNS data if you are going to use static IP addressing and these can be found in the network preferences when your MacBook Pro is on.

SHARK!

OK, try this. Go to PREFERENCES and then choose SHARING and switch on INTERNET SHARING. See if this helps.

SHARK!

How about getting a wireless router? You should be able to connect the router to the ethernet cable. The router would be assigned the static IP address and in turn would assign local ip addresses to the items on it's own network.

The Internet Sharing should work. I don't use it myself but I tried turning it on and it behaved as expected.

Try turning the internet sharing off and even turn the wireless off too so you're left with just the ethernet active on your macbook. At this point is it safe to assume you have a working connection? The static IP address you are assigned, is it one in the private IP range?

If you turn off cellular data on the phone the only way you should be able to do stuff like browse the web etc is if you have a working wireless connection. Try turning the internet sharing back on, ensuring you are sharing the ethernet connection to the wireless, so ethernet in the drop down menu and AirPort ticked. Maybe even try changing the network name and using WEP in the AirPort Options. WEP is crap but who knows, maybe your mac will be more willing to share the connection if you do.

If it still isn't working try looking in Settings : Wi-Fi : and click the blue arrow to the right of your wireless connection (when you are connected to it). How does the IP address and Router compare to those assigned to the mac?