How to describe the practice of using "am-pluh-fi-key-shun" to indicate it's pronouncation? [duplicate]

This kind of pronunciation help is called a pronunciation respelling. Unlike IPA, it’s not actually a transliteration as such, since it doesn’t use one system of writing to represent something from a different system of writing: it uses the same system of writing to (attempt to) resolve ambiguities within that system itself.

The advantage of a pronunciation respelling is that the system is immediately familiar to anyone familiar with the language, since it uses the language’s own orthography as basis. The disadvantage, especially in a language like English, is that it is less precise and more likely to be ambiguous than a true phonetic transliteration which, as oerkelens points out, is language-agnostic and based on the acoustic/enunciatory details of each individual sound.

Wikipedia has a very useful article on pronunciation respellings for English, which has a tabular overview of some of the standardised respelling systems that are or have been commonly used for English.