I was doing some mixed tenses grammar exercises from the book "A Practical English Grammar Exercises 2" And there was such a part of a conversation:

Tom:.....I speak to Ann, please?

Ann: Ann (speak).

I think that it should be that way:

Tom: Could/Can I speak to Ann, please? <--------1

Ann: Ann is speaking. <---------2

But the answers:

Tom: Could I speak to Ann, please?

Ann: Ann speaking.

So please, could you explain me these two things? Why it isn't appropriate to use 'can' in the first sentence and why we can't use 'is' in the second sentence? And maybe someone could fix the mistakes I did in this message?

Thank you Emotion: smile
Welcome to English Forums, Zygis.

Why it isn't appropriate to use 'can' in the first sentence-- 'Can' is OK, but it is less polite than 'could'.

why we can't use 'is' in the second sentence?-- Her response is a semi-fixed phrase. Here are the possible options: Ann speaking / This is Ann speaking / This is she.
Thank you for helping me Emotion: smile

I was surfing the google for 'semi-fixed phrases' and I didn't get many useful results. So I wanna ask another question:

How can I Know when to use a semi-fixed phrase, maybe there are some rules, because I haven't found any.

Also, is it possible to learn those phrases?
Students: Are you brave enough to let our tutors analyse your pronunciation?
No rules, unfortunately. Fixed phrases, semi-fixed phrases,idioms, etc, are items you have to learn/memorize. They are vocabulary.