By or on?
What is more correct in a question to ask? " how to learn English by the cellphone?" Or " how to learn English on the cellphone" please if you can help me. I'm very grateful.

Question

Answer

How can you learn English on your cellphone? or Do you know of any cellphone apps for learning English?

In British English we've always called a cellphone a mobile (phone), nowadays it's just referred to as a phone. You could simply ask - do you know any apps for learning English?

Answer

Both of those sentences sound strange.. Do you mean learning English through English lesson apps on cellphones?