Hi Pelin, Sorry, I just saw your message today. Yes, they're basically both the same. If you want to really nitpick, I would personally say that 'talk over the phone' emphasizes the separation between the speakers more, but is a pretty nuanced distinction. But here is a rough estimation of the usage. You can see that "on the phone" is by far the more common phrase. https://books.google.com/ngrams/graph?content=talk+on+the+phone%2Ctalk+over+the+phone%2Ctalk+by+phone&year_start=1950&year_end=2022&corpus=en&smoothing=3 I hope that helps!

There is no difference. You can also say "by phone". You can say "Let's talk about it over dinner" or "at dinner" but you cannot talk about it "on dinner".

both

These two are quite similar. Both are grammatically correct, however the general conversational way to say it would be 'we'll talk on the phone'.