It looks like the class only sets digital I/O. To read digital I/O with labJack.m, the functionality will need to be added. You can add a function to read a single or multiple digital I/O using the Feedback command/response with IOTypes BitStateRead (single digital I/O) or PortStateRead (all digital I/O). If you need to set digital I/O direction use BitDirWrite/PortDirWrite.
Most of the labJack.m class functions that are interacting with the U3 are using the Feedback command/response, so you can use those functions' code to help implement new functions in MATLAB. The low-level Feedback command/response packets are documented here:
C examples are here and help demonstrate setting up command/response packets and parsing out the the data: