The back-side Phillips is the most common version of the Phillips screwdriver on a Swiss Army Knife.

A #2 Phillips driver is located on the back of the knife in the place that the corkscrew occupies on many models.
Several models of Swiss Army Knives differ only by their inclusion of either the back-side Phillips or the corkscrew (eg the Spartan vs the Tinker). The design of the knives/tools does not allow both to be included.

The Phillips screwdriver was invented by Henry Phillips in the 1930's with the intention of providing a safer alternative to the traditional straight-edged screwdriver. Henry Phillips wanted a screwdriver that would prevent a damaging process called over torquing. This feature is also its weakness.

Victorinox

The back-side Phillips is available on 84, 91 and 111mm models.

This tool was introduced into Swiss Army Kinves in the early 1950s, and there have been at least five evolutionary versions produced, although the number may be closer to eight!.

The original versions have a squared off shank rather than the round (cylindrical) one used today, and might have been slightly larger than the current #2 Phillips. Early vintage versions have a file cleverly incorporated into the inner flat side.
In the mid-1970s the Phillips screwdriver had a slot cut into it to create a can-key, that is used as a key to open food tins designed to be opened by removing a metal strip from around the can - see diagram below. These tins were quite popular in the 50s through the 70s.
The current round tool was introduced round about 1980 and is slimmed down from past versions and shaped to fit a wider range of screw heads. The can-key was withdrawn in the early 1990s which can help with dating models.

Other Phillips drivers:

The in-line Phillips is another common version of the Phillips screwdriver available on some models.
The regular can-opener tool has a small slotted flat tip that is designed to be used with small Phillips screws, as well as small slotted screws.
The 58mm cap-lifter has a small #00/#0 magnetic Phillips driver.
The bit-driver is the most recent tool that contains Phillips, pozidrive, hex and slotted bits.