Basically you are making a network connection via bluetooth. Depending on the OS you drive, there's probably a guide such as [1] to set up bluetooth via the modem adapter to act as an internet connection.

Of course it relies on both devices being able to create and maintain a good bluetooth connection.

It would be nicer if phones could run two wifi networks at the same time, allowing a mix of leach or hotspots but I guess in practical terms it's only one in a thousand type of demand.

[1] https://www.lifewire.com/internet-on-laptop-with-a-bluetooth...