It is a transitive verb phrase because it needs to be followed by a direct object.
Get rid of.
(It is incomplete because it does not refer to an object.)
Get rid of those dirty shoes!
("Get rid of" is referring to the shoes.)
Get rid of that!
(Even though the noun is not specified, this sentence is still okay because it has a direct object in it, "that".)
So, it is a transitive verb phrase.