Is the sentence "I tried charging my phone, but in vain" correct? [closed]

Is the phrase "but in vain" correct to use as a dependent clause?

People often use an independent clause, "I tried charing my phone, but my efforts were in vain", or "I tried charging my phone, but it was in vain", in order to be clear. However, the way you have it, with a dependent clause, is not grammatically incorrect.

The expression "in vain" is inherently dramatic, and since it's ironic to have it applied to something as trivial as charging a phone, it sounds odd that you toss it off so lightly. I would instead play up the "hopeless futility" aspect by adding something like:

I tried to charge my phone, but alas --it was all in vain.

Still, there's nothing wrong with your sentence.