Over the phone vs On the phone

Is it OK to say 'talk over the phone'? If so, is it very conversational?

I will later find the quote from one of the books i've encountered 'over the phone' phrase.

Yep :)

"Over the phone" is used more in the past tense. It's rarely used in the present.

"I was talking with Bob over the phone" (On the phone is still correct)
"I'm on the phone, shut up!" ("I'm over the phone" is incorrect)
"I'll be talking with Bob on the phone tomorrow." (Over the phone here is also correct, but I don't hear it often)

Thanks, Pippynip!

I can now quote the sentence I was referring to:

On the nights that I was in Springfield, we'd talk and laugh over the phone, sharing the humor and frustrations of our days apart, and I would fall asleep content in the knowledge of our love. (Obama, The Audacity of Hope)