Essentially, a clause has a subject and a verb. Sometimes, a clause can stand on its own as a sentence (making it an independent clause), and sometimes, a clause can’t stand alone (making it a dependent clause). Here are a couple of examples: 1. The dog is sleeping, and you shouldn’t wake it up. (There are two independent clauses at play here.) 2. If the dog is sleeping, you shouldn’t wake it up. (The first part is a dependent clause, and the second is independent.)
By contrast, a phrase does not have a subject/verb combination and typically adds information to the sentence. Here are a couple of examples: 1. The dog is sleeping in the living room, and you shouldn’t wake it up. (The phrase here is “in the living room,” which contains neither a subject nor a verb.) 2. The dog had been sleeping in the living room, but, after hearing the garage door open, it woke up. (Even though “after hearing the garage door open” might seem clause-like because it has a verb, there is no subject, so it’s simply a phrase.)
If you find yourself with an assignment like my son’s, hope these examples can help. Good luck!