Question

1. I am calling instead of Mr. Frank.
2. I am calling in place of Mr. Frank.
3. I'm calling on behalf of Mr. Frank.
4. I'm calling in lieu of Mr. Frank.
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Are they all the same in meaning?
Which ones are commonly used? Do you have some other similar expressions?

Answer 1

Yes, they all mean the same thing. We would use #3 most often, though.

Answer 2

Well, although all four ways of saying it might be intended to mean the same thing, they could be interpreted differently. If you are speaking instead of Mr. Frank, perhaps you are speaking for yourself, not Mr. Frank. If you are speaking "on behalf" of Mr. Frank, that is clear that you are representing Mr. Frank and what he might say.