如何区别on phone和by phone？

on phone在电话里
mary,hurry up,you are wanted on phone
by phone电话边there is a book by the phone
或是通过电话he asked for help by phone

on有使用中的意思，所以on phone指正在通话中
比如说：on air指现场直播
by有通过的意思，所以by phone指通过电话……
比如说：by car,by bike
by还有一个用法，就是可以加差值，比如说表快了几分钟，也用by

on phone是 聊电话
by phone是 打电话