Turn off phone at night.

There is nothing wrong with that. If you want to leave it on and you have it set up for an iCloud backup, it will occur over night.

Hello,

In addition to kb1951's comments, see this:

Many people consider it a best-practice to put the phone on a charger overnight:

1. You start the new day with a fully charged phone
2. iCloud backups occur automatically (assuming a Wi-Fi connection)
3. Software updates occur automatically (assuming a Wi-Fi connection)
4. If something bad happens overnight, you know where your phone is and it is at least partially charged 

Good luck.