It really depends on what phonemic trasncript you wanna use. THere is the official english phonemic chart which is for example here: Phoneme chart: English vowel and consonant sounds for phonology and language study
There are many versions of it since every language has different types of pronunciation. For example Czechs, like myself, use often a very diffrent than the one above.
As for your inquiry about pronunciation of "x", i use kind of /egz/.
i am a teacher.