Answer:
The answers are indeed:
1. , where we often go to relax, --> nonrestrictive clause
2. by the door --> restrictive phrase
3. , a good friend, --> nonrestrictive phrase
4. that my mother used to tell me --> restrictive clause
Explanation:
First, let's differentiate a clause and a phrase. A clause has a subject and a predicate while a phrase does not. We can say a phrase is just a group of words that has a meaning.
From the description above we can already conclude this much:
1. , where we often go to relax, --> clause
2. by the door --> phrase
3. , a good friend, --> phrase
4. that my mother used to tell me --> clause
Now, the difference between restrictive and nonrestrictive is how essential that information is for the general meaning of the sentence. If removing the information does not affect the meaning, then it is nonrestrictive. If it does, it is restrictive. Nonrestrictive clauses and phrases are set off by commas. Therefore:
1. , where we often go to relax, --> nonrestrictive clause
2. by the door --> restrictive phrase
3. , a good friend, --> nonrestrictive phrase
4. that my mother used to tell me --> restrictive clause