Cell Phone - Math/Science
Using your phone as a calculator in a math or science class may be an appropriate use of your phone, but it depends on the class and/or the teacher. Your chromebook does have a Calculator app built in, so use that as an option first, then a calculator as a second option.
If the teacher wants you to learn basic calculation skills without outside assistance, using your phone or a calculator is not an appropriate use of technology.
Your teacher should either give you clear directions on when you can use your phone or you should ask. Do not presume that you can, just because another math or science teacher allows it.