Yes, it's possible to use your phone as a modem, connected to the tablet via a USB cable, as long as you have
(1) an APN from your network operator to make a data connection via their network, and
(2) suitable device drivers for the phone. On Windows, smartphones are plug and play, but I don't have any experience using them with Android.
On the tablet, you also need some software to control the modem - something like the Mobile Broadband Connect 3.0 application listed on here
You can write a simple connection app yourself using the Android Telephony Manager.
Alternatively, you could connect manually, using AT commands with a suitable AT command program (in Windows, it would be Hyperterminal). This thread describes a possible equivalent for Android.
Standard AT commands to make a data connection are described in the 3gpp TS27.007 specification.
There are a lot of variations for different manufacturers, but making a simple connect should be possible using the standard commands.