How to address in-group bullying without compromising PhD/career?
I have spoken to … but have not wished to pursue any formal complaints procedures out of fear my supervisor will compromise my PhD … and ruin my ability to work in research … 


Okay, so I am going to be the bad-guy here.  What you say you fear will happen here has already happened.  What you describe ---if accurate--- is already massively compromising your PhD and your ability to research.  The university has formal mechanisms in place to deal with this kind of issue.  If you are not willing to avail yourself of the mechanisms in place to deal with these problems then there is nothing that anyone can do.  (And frankly, it is quite difficult to muster sympathy for complainants who refuse to make a proper complaint when avenues are available for this.)  You should have complained formally or got out years ago, but since you are still there you have a choice: use the mechanisms available to you for complaints of this kind, or not.  Do not become a victim of the sunk cost fallacy.

If you decide to avail yourself of the complaint mechanisms at your university, the main thing you should do is this: document, document, document.  Document everything well, and collect and keep all relevant evidence of treatment that is unfair to you.  Make a chronological list of incidents, since the start of your candidature, detailing dates (or rough dates if you can't remember exact dates), what happened in each incident, and any documentation (emails, etc.) that constitutes evidence of the incident.  Write this in a neutral factual way, but make sure you briefly explain how each incident negatively affected your candidature.  Seek written statements from other sympathetic students that can back up your assertions.  You have said that the university has breached its policies when dealing with you.  Make sure you document instances of this as well.  If that is correct, then the university will be in a weak position in respect to the conflict, and you have a greater prospect of extracting some reasonable concessions in a complaint process.