Can I use Microsoft cloud for phone backup

No. An iPhone can be backed up to iCloud or to a computer. How to back up your iPhone, iPad, and iPod touch - Apple Support

However you can save files to Microsoft OneDrive or use the OneDrive app to sync some data to OneDrive, See: https://apps.apple.com/us/app/microsoft-onedrive/id477537958

Steve0615 wrote:

Can I use Microsoft cloud to backup phone

Doubtful.

What did Microsoft say when you asked them?