Why is the ICAO prefix for Alaskan airports "P"?
Definition from wikipedia:

The ICAO (/ˌaɪˌkeɪˈoʊ/, eye-KAY-oh) airport code or location indicator is a four-letter code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators are used by air traffic control and airline operations such as flight planning.

https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/ICAO_FirstLetter.svg/1200px-ICAO_FirstLetter.svg.png

This is a map of every ICAO airport code wordwide.

Alaska has PA, PF, PO and PP as airport codes. P = Eastern North Pacific.
PA=USA (Alaska) (also PF, PO and PP)

There is no special meaning behind the letter P and these codes, it's just a classification!!