I would like to compare two search phrases but on Google Trends it doesn't give any results. Is there any alternative?
There are lot of keyword suggestion tools available. Google and yahoo also offer free keyword suggestion where you will have the search data for the given keywords. However, you can't rely completely on the data but you can have an overview of trend.
It has nothing to do with the number of words, but the search volume. But yeah, I would imagine four word keyphrases wouldn't get searched much.