Just to add to what WR has already said: In general, although morph and phase can technically usually be interchanged, in general usage these days 'morph' usually applies to a cultured (ie man-influenced) mutation and 'phase' usually applies to a naturally occurring variation. For example, although you may find the odd albino python in the wild, we'd be more likely to refer to an albino Darwin carpet as an albino morph rather than albino phase. Where it gets confusing is when you have true polymorphic species. Polymorphic simply means that the animal naturally comes in a variety of types (usually different colour patterns) that aren't necessarily geographical variants. Although the word 'morph' appears in polymorphic, you'll rarely hear of these naturally occurring variations being referred to as morphs these days, but rather 'phases'. Lace monitors are a good example of an Australian polymorphic species - you'll find mixed populations of both 'normal' and broad banded lace monitors, fully interbreeding, in the wild. The broad banded ones are generally referred to as 'Bell's phase' rather than 'Bell's morph'. However, if some reptile keeper got ahold of a lace monitor that had an all-yellow mutation and line bred it, the offspring would likely be referred to as 'lutino morph', 'canary morph' or something like that, rather than yellow phase.
