Encrypting iPhone Text Messages

While iMessage is an end to end encrypted service, your cellular service provider's SMS text service is not.

The only way to get encrypted text messages is to use one of the internet messaging services like iMessage, or WhatsApp, Wickr or others. Google Hangouts encrypts in transit but does not store texts as encrypted once on the Google servers.

No. iPhones are intended to be personal devices, not shared devices. So the only protection is the initial passcode. You can create encrypted notes, and paste content into those notes, including copied texts.

They are already encrypted. You do not need to do anything to encrypt them.

Your entire device is protected by your passcode and Apple ID that only you should know. Apple does not provide a tool beyond these tools. Add 2FA if you don't already use it.

No there isn't. The iPhone is designed to be a single user device, and the passcode on the device is designed to keep others out of it and snooping at your content.

2 Factor Authentication.

See >>> https://support.apple.com/en-ca/HT204915