1. The offset of one's waking-sleeping schedule with respect to the standard 24-hour cycle; a useful concept among people who often work at night and/or according to no fixed schedule. It is not uncommon to change one's phase by as much as 6 hours per day on a regular basis. "What's your phase?" "I've been getting in about 8 P.M. lately, but I'm going to wrap around to the day schedule by Friday." A person who is roughly 12 hours out of phase is sometimes said to be in "night mode". (The term "day mode" is also (but less frequently) used, meaning you're working 9 to 5 (or, more likely, 10 to 6).) The act of altering one's cycle is called "changing phase"; "phase shifting" has also been recently reported from Caltech.
2. "change phase the hard way": To stay awake for a very long time in order to get into a different phase.
3. "change phase the easy way": To stay asleep, etc. However, some claim that either staying awake longer or sleeping longer is easy, and that it is *shortening* your day or night that is really hard (see wrap around). The "jet lag" that afflicts travelers who cross many time-zone boundaries may be attributed to two distinct causes: the strain of travel per se, and the strain of changing phase. Hackers who suddenly find that they must change phase drastically in a short period of time, particularly the hard way, experience something very like jet lag without travelling.