The police might seize all sorts of evidence in a criminal investigation, from the accused's own property to that of his family, employer and even the victim – the owner does not have to be charged with a crime to have his phone, gun or other property held. You are always entitled to your property back when the case if finished. The only questions are how, and when.
TL;DR (Too Long; Didn't Read)
You have to wait until the case is definitively over before you can get back property held for evidence. There's a short window for claiming your items in some jurisdictions.
About Property Seized as Evidence
Unlike property seized as contraband, property seized in evidence is not confiscated from the owner. Rather, it remains in the safe custody of the police and the district prosecutor until the criminal case is over. While you may be able to reclaim your property early in some circumstances – for example, if you can persuade the police that having your phone is absolutely essential to your job – most times, you'll have to wait until the case is definitively over. This includes time spent on appeal which may run to many weeks, months or even years. It's worth mentioning that when the police seize contraband items like illegal weapons and drugs, you can't expect to get them back. Law enforcement is likely to destroy these items.
You'll Get a Receipt
Whenever the police take property into evidence, they provide you with a receipt listing all the items they have in their custody. When the police seize evidence during a search, the receipt is called a "search warrant return." The return lists all the items taken, including the date of seizure, a police inventory number and the identities of police officers involved. In most jurisdictions, the police will file a copy of the search warrant return with the court clerk's office within a few days of executing the search warrant. You can get a copy from the clerk's office. If the police issue criminal charges against you, your attorney will receive a copy of the return in the lead up to the criminal trial.
The Clock is Ticking
Getting your property back from the police is as simple as asking for it and producing your receipt and photo ID. In some states, you might also need a release from the district attorney's office; call the office at the end of criminal proceedings to request this document. The catch is that there's a ticking clock – in some jurisdictions, you have a limited number of days to request the return of your things after the criminal case ends. In New York City, for example, the period is 120 days after the termination of criminal proceedings. If you don't claim your property in this time, the police have the right to dispose of your items.
File a Petition for Return of Property
If the prosecutor refuses to grant a property release and there's no obvious reason why the items are still needed as evidence, the only option is to file an administrative petition with the court. This isn't a legal tool for the average citizen to use on her own, so you will need to hire a lawyer. The judge will hold a hearing to figure out why the property is still in custody and what should happen to it going forward.