My DD (class of 2021) did not take calculus before attending USMMA, and she did fine. You will take a math placement exam during INDOC, and your score will determine what math you take. There is plenty of extra help available, the professors will work with you, and your fellow midshipmen will share their knowledge as well. You may have to put in more study time than some of your classmates, but you should be fine.
Regarding phones, the rules may vary by what company you are in. You will be given phone privileges after INDOC as earned by your company as a whole. Phone privileges have become more liberal in recent years, and most companies allow you to keep your phone within weeks of the start of the academic year.
You will not be allowed to leave campus as a plebe until Parents Weekend which is in October this year. (The exception is for sports team movements.) Your first week-long break where you will have leave to visit home is after first trimester, usually around the first week in November.