We recently lost a case in court and found out later that the chief judge had links to the respondents and our expert witness. Can I subpoena mobile phone records to prove they contacted each other?
Possibly. How did you find out, and what evidence is there the judge had links to the parties?
Phone records may not be sufficient evidence of bias anyway. In small country towns, and at the top end of town, judges often know various parties and that is often not enough by itself to disqualify a judge from a case for apparent or actual bias.
There is a lower threshold about whether the judge should have advised you during the case they knew the other parties.
If you are considering an appeal be aware of the time limits in which to initiate an appeal.