The complete verbal phrase in this sentence would be singing in the trees, and its type is participial.
A verbal phrase can be participial, gerund, or infinitive, and there are no gerunds and infinitives in this sentence.
I stayed up all night doing homework, however i just couldn't concentrate.
I'm not sure but I think it's either:
'That gallant spirit hath aspir'd the clouds.'
Or
'Romeo: this days black fate on more days doth depend.'
Or
'This but begins the woe others must end.'
Because they sound like they are mentioning about the future play/life, they are not deliberately saying it, they are speaking in clues and hints.
Hope this helps in anyway possible. (Haven't done this play in 3yrs. And bad in the quotes, but u hope this helps.)