Received this in a text from a Chinese friend. I want to say that "了" here is not part of the verb phrase but instead just an emphatic particle, same as if you said something like "我最怕蜘蛛了"。Then again, that's not something I would ever think to produce, it just sounds more normal that way to me. Does anyone have a more authoritative answer?
In a phrase with this construct:
可/太/最 + [adjective/adverb/stative verb] + 了
了 serves as a modal article (rather than tense particle) to express emphasis and is optional.
"我最怕蜘蛛了" totally equals "我最怕蜘蛛" from the perspective of grammar and meaning. "了", which is similar to "喔", "吧" and "呀", is an auxiliary word that can be omitted because it doen't have any meaning, but it's very weird to omit it in some situations. Unfortunately, even native speakers can't tell you the exact rule of when to use this auxiliary word.
Generally speaking, you should use it when you are speaking and omit it when you are writing. Basing on the same logic, you should use it when you are writing someone's talk. for instance, you should write
However, please remember that it's "general speaking". I am sorry that it's very hard to tell you the exact rule.
As I native speaker, I would say that "了" is mainly used to help with expressing an emotion.
I love you the most
where "了" helps express affinity toward someone. Sometimes "了" is also used to express the 'donenness' of an action.
I have eaten
where "了" helps express perfect tense.