iPhone 6plus freezes randomly

If the freeze doesn’t appear to happen with respect to a certain operation or App (if it does then try deleting that App which also removes it’s data), I would try the following.

Firstly try a Forced Restart https://www.macworld.co.uk/how-to/iphone/how-restart-iphone-or-ipad-3662903/ and see how things go.

If still having issue then try Restoring your device, this can be done via iCloud iCloud: Restore or set up your iOS device from iCloud but if you have a Computer it’s probably easier/quicker via iTunes Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

It goes without saying you need to make sure you have a recent “BackUp” required for which ever option you try.

If a Restore also fails then do same again but this time set your device up as “New”, this has been known to resolve some tricky issues mainly related to data corruption which could be reintroduced from the “BackUp”, but then your device will be a blank slate and will require you to manually set things up again. If Photos, Calendar, Contacts and Mail are in the cloud you should be able to sync them back down, but Messages for example will be lost until Apple brings that cloud option to us in (hopefully) the next iOS update.

If non of the above works then contact Apple, tell them the troubleshooting you have tried and see what they say.