If you had iCloud Photo Library turned on, deleted photos are in the Recently Deleted album on the device and on iCloud for approximately 30 days and can be recovered from there. iCloud Photo Library - Apple Support
If you didn't have iCloud Photo Library turned on but do have a backup from when the photos were on the device, you can restore from the backup. Note that the restore replaces all data (not just photos) currently on the device with the data from the time of the backup. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support