In this sentence, _do obey_ is the verb phrase.
In interrogative sentences, the verb phrase is inverted and a part of
the verb phrase is placed first and the subject after. For example:
Will you go with us?
_You_ is the subject of this interrogative sentence and _will go_ is the
verb phrase; but in order to ask the question, the order is inverted and
part of the verb phrase placed first. In using interrogative adverbs in
asking a question, the same inverted order is used. For example:
When will this work be commenced?
In this sentence, _work_ is the subject of the sentence and _will be
commenced_ is the verb phrase. If you should write this in assertive
form, it would be:
This work will be commenced when?
By paying close attention we can easily distinguish the verb phrases
even when they are used in the inverted form or when they are separated
by other parts of speech.