Difference between 'my name is X' and 'this is X'

[Phillipo]

English Language Tests, Intermediate level

ESL/EFL Test #112 "Placing an order via phone", question 8

To-go specialist: Thank you for calling Motzeralla's 'to-go'. ......... Amy, how can I help you?

(a) I am
(b) Here is
(c) My name is
(d) This is

English Language Tests, Intermediate level

ESL/EFL Test #112 "Placing an order via phone", answer 8

To-go specialist: Thank you for calling Motzeralla's 'to-go'. This is Amy, how can I help you?

Correct answer: (d) This is

Your answer was: incorrect
To-go specialist: Thank you for calling Motzeralla's 'to-go'. My name is Amy, how can I help you?
_________________________

Why is it incorrect to say 'My name is Amy' on the phone? or
What is the difference between 'my name is X' and this is X'?

[Mister Micawber]

.
This is + name is the fixed expression for identifying oneself via telephone. My name is + name is occasionally used also.
.
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Native English teacher at Mister Micawber's