No matter how good is your grammar, you can't communicate without words. A strong vocabulary is essential in conveying your ideas effectively and persuasively. Besides, many standardized "verbal ability" tests are in reality vocabulary tests.
Many ESL students find English phrasal verbs somewhat challenging. Phrasal verbs are usually composed of two or three words joined together to act as a single verb. Phrasal verbs are an important part of the English language and are commonly used in our day-to-day lives.