if I'm a witness in a civil suit can the defense search my phone records and charge me for separate crimes.

It seems unlikely to me that the phone records of a witness would be relevant to a civil case, but if they are then the Court may order that they be disclosed.  While only the government can charge you with a crime, if your phone records show evidence of a crime, the Court may refer the matter to the police or district attorney for further criminal proceedings.  Again, this seems very unlikely to me but, without knowing any details, I can't say it is impossible.