char *sql="CREATE TABLE PhoneNote(ID integer primary key autoincrement)；
sqlite3_exec(phone_db,sql,NULL,NULL,&errmsg);
sql="INSERT INTO PhoneNote values(NULL)";//这一句用mprintf怎么赋值？
sqlite3_exec(phone_db,sql,NULL,NULL,&errmsg);

char *sql = NULL;
sql = sqlite3_mprintf("insert into PhoneNote values(NULL)");

这样应该可以了！