If you forget the phone's password you will need to ''restore the phone'' back to its original setting. Your phone would need to be synced with your Google or iTunes account so as not to lose any data. On the other hand, syncing your phone with these cloud providers means that there is a duplicate of all of your data in the cloud.
If you just want to encrypt your messages on the phone, please refer to use [[Protect files and messages https://play.google.com/store/apps/details?id=org.thoughtcrime.securesms&hl=en TextSecure] on my phone]Android and [https://itunes.apple.com/ca/app/signal-private-messenger/id874139669?mt=8 Signal]on iPhone
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