Hello Jun,
It is true that in colloquial spoken English you may not hear the least important words of the phrase. This is particularly common with 'got' phrases, and introductions and not so common with others. e.g.. "got it!, got some?, got everything?" or "alright? everything ok?" etc...
HOWEVER, this is only spoken english and does not apply to written versions of the language.
In English it can often APPEAR that we are not saying a word in a phrase because we only STRESS the most important words in a sentence. So, if spoken fast, can be misinterpreted to omit certain words when, in reality, they have been spoken but just not heard.... I hope this makes sense?