I erase a phone in accident how can I get back

Restore from backup

To restore from backup see:

iOS: Back up and restore your iOS device with iCloud or iTunes

If you restore from iCloud backup the apps will be automatically downloaded. If you restore from iTunes backup the apps and music have to be in the iTunes library since synced media like apps and music are not included in the backup of the iOS device that iTunes makes.

You can redownload most iTunes purchases by:

Downloading past purchases from the App Store, iBookstore, and iTunes Store

what if my phone is lost and i erased it from find my phone

If you erase then find your iOS device, you can restore the information on the device using iCloud Backup (if backup was turned on before you erased it) or iTunes. For more information, see iCloud storage and backup overview, or the “Safety, handling, and support” section of the iOS user guide for iPhone, iPad, or iPod touch. For a device that doesn’t use the latest iOS version, get the user guide for iPhone, iPad, or iPod touch from the Apple Support manuals website.

https://support.apple.com/kb/PH2701?locale=en_US&viewlocale=en_US