I use WordWeb which is available online for vocabulary. But, is there any equivalent for getting the meaning and origin of phrases ?
The online dictionary Wiktionary aims to be a dictionary of phrases as well. It is a project in progress, but it does have very many phrases already, e.g. kick the bucket or when Hell freezes over and about 60,000 others.
They also have an "appendix" that contains fewer phrases, if you'd like to just read through.
In haste: what kind of phrase are you thinking of? An example would help us to chart the routes. If you are looking for short or very common phrases, or expressions/idioms, those will be in on-line dictionaries. If the phrase is none of those (then what are they?), I doubt whether there is a database with phrases that also contains rephrasings. However, my advice would be to simply Google your phrases: you will usually be able to divine their meaning with the results, through context and the dictionary entries that you will often still get. Make sure that you enclose your phrase in double quotation marks.
You might try http://idioms.yourdictionary.com. I don't imagine it outperforms Wiktionary for breadth of content; it only boasts about 10,000 idioms on record in its print version. It also appears focused on American English only. However, you can browse the contents by proximity to a given search, which can prove useful if you're a writer or editor.