Answer:
-2
Explanation:
If Issac has finished 8/10 problems in the homework, and Phil has completed all of it, it can be concluded that Phil completed 10/10. 10/10 would equal a whole, or in this case, the entire homework. If Issac completed 8 problems, and Phil completed 10, subtract both values to find that Issac completed -2 more problems than Phil.
*correct me if I'm wrong, or If I didn't fully understand your question, because I am a little confused with how much homework Phil has finished.