While studying, I faced these two sentences:
I come to Istanbul on the train every week.
I came to Istanbul last week by train.
I want to know is there any differences between the phrases 'on the train' and 'by the train?'
Both phrases mean the same thing. In my area of the US, they are used interchangeably.
It is always 'by train' and never 'by the train' though.
The phrase 'by the train' would mean the same as 'near the train'---quite a difference in meaning. A native speaker would probably recognize the mistake in context, as it is a common mistake for non-native speakers.