Trademarking only the word does not protect the rest of the phrase. For example, say you trademark the word "Fizzbin" and use it in the phrase "Fizzbin for the all the finest things!" In that case, if you only trademarked the word, someone else could use the phrase "Gronk for all the finer things!", etc. Trademark anything that is trademarkable that you feel has value and is sufficiently original, non-generic or -description, etc. to be trademarked, for the broadest possible protection.