I lost my iphone but it was power of how can I get

See these two support documents.

If your iPhone or iPad was stolen - Apple Support

Find your lost iPhone or iPad - Apple Support

If the device was off, it will not be able to be tracked until it is turned on. However, follow the steps online for putting it into Lost mode and when it is turned on it will be locked.

If the device was off, it will not be able to be tracked until it is turned on

iPhone models since the iPhone 12 will send out a very brief intermittent Bluetooth signal that can be picked up by other iOS devices in close proximity. Those other IOS devices will forward location information to Find My.

If the battery has a decent charge when the phone is powered off, it will send out that very brief intermittent Bluetooth signal for weeks before the battery finally runs down.

"I lost my iphone but it was power of how can I get: Lost iPhone"

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Troubleshooting a Lost iPhone:

A. For Find My:

Is Find My enabled? IF so, locking it with it would be wise. To learn how Find My works, go here: Use the Find My App to Locate a Missing Device or Item - Apple Support

B. Backtrack your Locations:

If you were at a retail store or local cafe', then stop by and see if if was placed aside by the store manager. You never know. Lost items before, and the retitler placed in an a safe location.

C. Text the iPhone a Message:

If you cannot find this, then text the iPhone, sending it a messages asking whomever finds it to contact you. Perhaps, have them eMail you, putting a particular title in it (so that you recognize the eMai)l. If you go to pick it up from an individual, then have someone there with you, probably meeting them at a public, safe location, both for safety purposes.

D. Also, Contact Local Authorities:

Perhaps someone is respectful enough to have turned-around handed it over to local authorities. See if they have found it.

Thanks. Forgot about that new feature.

This assumes that "iPhone Findable after Power Off" is enabled, which is the default setting on the iPhone.