Breaking down meaning of 几句话
Pedroski wrote in his answer:


  After enumeration, such as '几‘， any word you can't explain will be a classifier.


Agree with that.  "句" in "我想对你说几句话" is not a noun but a classifier

If you say 我想对你说几句, you  just omitted the object "话" but it is still implied. Similar to saying "may I have a few?" in English, which an object is implied,

For example, a man is eating candy, his friend pointing at the candy and ask: "May I have a few?" he doesn't need to state the object "candy" which is understood by both parties 

With the same logic, the object in 我想对你说几句 is made understood with the present of the verb "说" (say). The object of the verb "说" (say) is always "话" (e.g. 真心话, 不中聽的话, 重要的话 etc.)

Example of "句" as a noun: 


with classifier: 一個句 (a sentence), 個 is a legit classifier for 句(n)
with applicable verb: 造句 (make a sentence), 造 is a verb applicable to 句(n)
with applicable adjective: 疑問句 (interrogative)


疑問句 (interrogative) is a single term, but 疑問 functions as an adjective and 句 functions as a noun within the term