Phone patching is certainly a part of amateur radio, but your question does not describe how a telephone circuit element should be at all related to “[creating] a portable field radio”. I recommend editing your question to give the context you gave here, and also to explain what your goal is — why do you want to incorporate telephone circuits into a radio, if it is not for the purpose of phone patching? Or are you asking a more theoretical question?
- Do you mean that you want to create a wired telephone system in the field that's linked by radio elsewhere?
- Do you want to know whether this particular circuit is used in radios' audio or RF circuits?
- Do you want to know how a phone patch system works electrically?
All of these are reasonable questions, more or less, and they are much more specific and answerable than "how does this circuit relate to amateur radio" — especially as it sounds like you already know how it might relate to amateur radio (by being part of a phone patch).
Make sure to edit your original question — don't just explain here on Meta.