There are several conventions for phonetic transcription using the Cyrillic script, typically augmented with Latin and Greek to fill in missing sounds.
The details vary by author, and depend on which letters are available for the language of the text.
For instance, in a work written in Ukrainian, ⟨г⟩ may be used for [ɣ] (the voiced equivalent of ⟨х⟩), whereas in Russian texts, ⟨г⟩ is used for [ɡ].
Authors differ, for example, in whether they transcribe the voiced fricatives with the South Slavic letters ⟨ѕ⟩ and ⟨џ⟩, with the ligatures ⟨ꚉ⟩ and ⟨ԫ⟩ (which are common in monolingual dictionaries), or as simple digraphs ⟨д͡з⟩ and ⟨д͡ж⟩.
⟨ы̅⟩ here is a hack: the top line should connect the two parts of the letter together.