I do agree, with the ruling, with the interpretation, and with the usage and application in this case of the Fifth Amendment protections against self-incrimination. To explain:

I think personal papers implies that you have access to the data in the same form that it is used by the hypothetical original user, owner, or the defendant, in this case. The user of the phone operates it as an extension of their mind; try using someone else’s phone, and you won’t get the same utility or data out of it as the user. It is theoretically possible to extract all of the data and metadata from the phone, but you can’t correlate that with usage perfectly, and it’s hard to correlate it with user awareness or intent; contrast unfamiliar phones with questionable or incriminating documents or other kinds of files. The format implies usage of files. This is not so with phones or entire computing devices. A specific user’s behavior must be observed for intent to be accurately deduced. Simple possession of data does not: imply creation of that data, awareness of the presence of data, intent to use or pass on that data, and so on. It is reasonable to assume that with access to the device, its contents would be used contrary to the owner’s intent, and perhaps contrary to actual matters of fact. If eyewitness testimony can be fallible, so too can the testimony of a device against its operator, especially with a prosecutor involved. One could find themselves forced to deny baseless accusations, the foundation for which is based on the outcome of a search which ought to have never occurred, and which search should be inadmissible due to duress of being held in contempt of court being used to coerce a confession, admission, or testimony against oneself of some kind.

I also agree with the Fifth Amendment argument. If someone can compel you to open your phone, the only reason they would reasonably do so is to prosecute you or hold you in contempt in order to force the user to both acknowledge that they know the unlock code, and further force the user to defend against an unreasonable search of that which should be private. If the law can’t get it, they shouldn’t be able to twist anyone’s arm to help, especially the defendant. From the point of view of the law, this may seem just, but as a defendant, you can only give the prosecution data they don’t already have. The fact that if you are in this situation at all is why the Fifth Amendment exists to begin with. If your mind or will can be bent to your own prosecution, or force you to undermine your own defense by affirming knowledge about a device and it’s unlock code, via threat of imprisonment via contempt of court, I would see that a potential abuse of Fifth Amendment protections.

I view prosecutors advocating for violating or actually violating the Fifth Amendment through arguments leading to forced unlocks to be committing legal malpractice on behalf of the government; judges who accept these legal arguments are literally performing unconstitutional kinds judicial activism, as these interpretations of our rights functionally remove our inalienable rights via legal precedent. This should have never been allowed in the original case; as this Indiana case is part of appeals of that original case, the appeals courts have standing to rule that forcing device unlocks is inconsistent with the Fifth Amendment. This ruling is a step in the right direction. Now we just need a similar ruling by the highest court in the land, not just the highest court in Indiana.