Nevertheless, the tendency of the Phillips screw to cam out easily was later found to be advantageous when used with early power tools, which had relatively unreliable torque-limiting clutches. In this context, cam-out helped protect the screw, threads, and driving bit from damage caused by excessive torque.[4]: 85–86  A follow-up patent in 1942 further refining the Phillips screw design describes this feature and argues that if screw-driving clutches were perfect, a screw recess with zero vertical contact angles (and thus no axial cam-out force) could be utilized. However, it noted that such designs had proven unsatisfactory on assembly lines, as the driving bits would not disengage in time to prevent damage.[5

Cam out source

You're right it wasn't originally designed for it but later patents and iterations on the Phillips head driver specifically designed it in which is where I think the confusion comes from. I had always heard it was originally designed that way but I guess not.