Assuming you are using android and it has tethering as an option, this is not something you do on your computer.
In android, somewhere in the settings you should have the option to use" usb tethering". If you don't, you may need to install an app that does this for you.
Once you plug in your phone to Linux mint, you tap the "enable usb tether" button on your phone. Linux mint will automatically see it and use it.
I don't know how it works on iPhone.
On my old windows mobile phone, I had to dial into it with a phone number like an actual modem.
Sent from my Nexus 4 using Tapatalk 2
*Edited to remove duplicate attachment.
- uploadfromtaptalk1359237900118.jpg (72.49 KiB) Viewed 1009 times