The verb phrase in the sentence "I never understand physics" is "never understand".

Here's why:

* Verb: The main verb is "understand".

* Adverb: The word "never" modifies the verb "understand", making it an adverb.

* Verb Phrase: A verb phrase is formed by combining the main verb with any helping verbs (like "will", "have", "should", etc.). In this case, "never" is acting as an adverb within the verb phrase.