Breaker Trips Range

It goes by the current in each phase (or the the current in the maximum-current phase). The second example of 33.33 per phase will not trip the breaker.

A breaker has different tripping characteristics based on short time, long time, instantaneous and ground fault with respect to the current.

Simply put, a 100A Trip breaker, will start to open when it is experiencing more that 100Amps on any of its phase or wire connected to it.

There is nothing in a standard thermal magnetic circuit breaker capable of performing math*...

Each phase has it's own current sensing device. If the breaker says "100A thermal trip" that means that each current sensing device is calibrated to trip at 100A or more (sort of, we won't go into pick-up points etc. for this discussion).

If any one of the three (or 2) sensing elements in the poles sees a current that exceeds its threshold, the element activates the tripping mechanism and opens all poles.

* That said, it doesn't actually matter anyway. 100A through a 3 phase breaker is not 3 x 100A, it is still referred to as 100A. Common misconception.