verb (used without object), phreaked, phreak·ing.

to act as a phone phreak.

verb (used with object), phreaked, phreak·ing.

to tamper with (telephones) as a phone phreak does.

Origin of phreak

1970–75; altered spelling of freak1, copying ph- of phone1
Can be confusedfreak phreak Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for phreak

1972, originally in phone phreak, one of a set of technically creative people who electronically hacked or defrauded telephone companies of the day.

The phreaks first appeared on the US scene in the early 1960s, when a group of MIT students were found to have conducted a late night dialling experiment on the Defense Department's secret network. They were rewarded with jobs when they explained their system to Bell investigators. ... The name "phone phreak" identified the enthisiasts with the common underground usage of freak as someone who was cool and used drugs. ["New Scientist," Dec. 13, 1973]

The ph- in phone may have suggested the alteration, and this seems to be the original of the 1990s slang fad for substituting ph- for f- (e.g. phat).

Online Etymology Dictionary, © 2010 Douglas Harper