Step 1 is to get it working when you are actually on the LAN. Step 2 will be to fix any problems with VPN.
First, can you access BI camera views via the HTML interface from another computer?
Let's say your BI computer is 192.168.1.100 just for instance. On another computer, go to a browser page an enter this address:
192.168.1.100:81 (of course change the address numbers to match your BI computer's LAN address)
The :81 is important; this is the port used to connect to BI (at least on my installation; YMMV).
If that works, double check your app on your phone and make sure the :81 is appended at the back of the address.
If you aren't able to access BI from within your LAN using the proper machine address and port, it's probably a firewall issue. I once had a problem after a Windows update where I couldn't access it... it turns out that MS decided to switch my BI computer from thinking it was on a private network which it was, to being on a public network, which of course invokes more security blocks and such. I had to switch it back to being on a private network. Come to think of it, another computer I was trying to use to access BI also got switched to Public, and I had to switch that one too.
Also, just double check your mobile access credentials to be sure. We've all made mistakes there...

Let us know how it goes.