"Out-of-phase" is a somewhat ambigious term. The reason I say this is because an engineer can use phase to sculpt sound. That's the whole reason behind using multiple microphones for tracking. The result of that sound depends on the relationship of time arrival of the frequencies for each microphone i.e. their phase. Therefore, phase is a time relationship and if two sources simply don't sound good combined, one can think of this as their time relationships not complimenting each other or as habit has come to form the phrase "out of phase". You can see how it can be somewhat misleading because it scultping sound, sometimes we set mic's just so that certain frequencies are actually not in phase together for each mic and some are. It's really about the combination of in and out of phase that in totality creates "the tone".
FYI, the 180 degree flip on consoles or DAW are more akin to polarity which one can think of as direction (-/+) rather than time. Polarity is kind of an on/off thing where as phase has fine increments of time. Both however can interplay within signals of course. Both are important. Both take time to learn and understand and ultimately your ear tells you everything you need to know.
