Can I change my iPhone 14 backup to my iCloud account on Microsoft 365?

No, you can backup to either iCloud or a computer. This document outlines the various ways you can back up your iPhone, iPad, and iPod touch --> How to back up your iPhone, iPad, and iPod touch - Apple Support

Microsoft does not offer iCloud storage (iCloud is Apple's online storage). You may be thinking of Microsoft cloud storage, which is wholly different. Your iPhone can backup to iCloud or to your computer: How to back up your iPhone, iPad, and iPod touch - Apple Support

JoeyWro wrote:

Thanks. I'm trying to learn how to change WHICH iCloud account my phone backup uses. It's still iCloud - it's just my iCloud I got with Microsoft 365.

Microsoft 365 does not give out iCloud accounts. Microsoft 365 uses Outlook accounts which in turn have One Drive cloud Storage which has nothing to do with iCloud.

if you have an Apple ID account, that uses a Hotmail or Outlook email address as its identifier, you can log in to that in Settings ➡️ Account (top of settings) on your iPhone. The iCloud account would be tied the email address shown there on your iPhone. But again, this has nothing to do with Microsoft 365 accounts in any way shape or form except as a “user name” for the Apple ID:

This article hasn't been updated in 3 years but it may be worth reading Make a split library portable - Apple Community

iCloud is an Apple product. It has nothing to do with Microsoft or Office 365.

If you mean can you store backups on Microsoft’s One Drive “cloud” storage, then no, that is not possible.