The definition of a phrase is a sequence of words that do not form a sentence.
By "sequence" I mean they are normally in some order, or at least not separated by full stops or line-endings and such. So a list of words is not a phrase.
In some situations, it makes sense to include single words in what count as phrases, but usually a phrase consists of more than one word.
In certain modern branches of linguistics, a phrase is sometimes a sequence of words that form a constituent. But usually something like a noun phrase is rather a kind of phrase, a constituent phrase, as opposed to non-constituent phrases.
Your examples, however, could be said to be sentences, though not full or complete sentences: they can be introduced with a capital and ended with a sentence-ending stop, but they are probably not (full) clauses.
Good job!
Nice shirt!
You could say these are elliptical clauses and hence elliptical complete sentences, because they do not syntactically depend on any (other) clause and the omitted words can be easily supplied:
[You have done a] good job!
[That's a] nice shirt!
A clause is conventionally a phrase that contains a finite verb and (all) its constituents. In (certain recent branches of?) Anglo-Saxon linguistics, any verb will do, not just finite verbs.