The Bell System (America's telecom monopoly until it's breakup in the 80s) pretty much avoided Phillips, etc. screws. Everything was slot (or pin-hex tamperproof). I do see mention of a Phillips driver in this 1961 BSP: http://www.telephonecollectors.info/index.php/browse/bsp-bel...
The slotted terminal screws worked well because they were cheese head, or cylindrical, allowing the driver to apply torque at the very edge of the slot. Outside the Bell System, terminal screws are usually binding head, which has a fillet around the top edge, removing material where it's most needed.
The slotted terminal screws worked well because they were cheese head, or cylindrical, allowing the driver to apply torque at the very edge of the slot. Outside the Bell System, terminal screws are usually binding head, which has a fillet around the top edge, removing material where it's most needed.