Step 1: Recall the definition of a verb phrase.
A verb expresses an action or state. In compound tenses, the full verb phrase includes all auxiliaries and the main verb.
Step 2: Analyse the sentence.
"The Government has been reviewing the project for several years" uses the present perfect continuous tense, where "has been reviewing" is the complete verb phrase (auxiliary 'has been' + main verb 'reviewing').
Step 3: Eliminate incomplete answers.
"Project" is a noun; "several" is an adjective; "has" alone is an incomplete auxiliary. The full verb phrase is "has been reviewing".
\[ \boxed{\text{has been reviewing}} \]