Sorry, each motor connected to the same channel A on the DRV8835 showed the problem. I checked both motors directly with the power supply anyways, and they work in both directions.
With APHASE and BPHASE connected to ground and AENBL and BENBL connected to 5V, channel A motor is spinning clockwise and channel B motor is spinning counterclockwise. Which is odd because the robot would be driving in reverse when I expected it to be driving forward. When I plug in APHASE and BPHASE to 5V, both motors stop.
I believe I have the same problem as the guys in this thread. I am able to run the operating modes of IN/IN mode on channel B even if the mode pin is driven high and I have the same direction problem with channel A. So I guess something about my setup damaged the board? I have a spare DRV8835 board so I would like to know what may have happened before I use it.