Excel & iCloud Drive Syncing

I have Office 365 installed on my MacPro, and the Excel App installed on my iPhone.

I use iCloud Drive to store the files that I use between these devices, but I am having a right mare with either device picking up the changes I made.

For example, I changed a few colours of the cells on my Mac, then saved and closed. When I open the same file on my iPhone, it then doesn't pickup the changes that I made. Instead, it then overwrites the file in the cloud with the phone version, thus losing the changes I made when I re-open it on my Mac.

When i open the iCloud Drive App on my phone, I cant find a "Open With" option, so by default it opens in a basic view (with no formatting). When I click on the "Share with", and select Excel from the list on my Phone, I get a message saying that its "Read Only" and no changes can be saved.

I have over 20GB worth of iCloud storage left, the Excel file (*.xlsx) is only 16.335Kb, and I have a 75mb/17mb Internet connection with both the Mac & iPhone running on a 5Ghz network. I am signed into iCloud drive using the same Apple ID on both devices. I have 92GB free on my iPhone 7, and I have the 512GB flash storage on my Mac, which is pretty empty.

Is there a better/faster way of syncing Excel files using iCloud drive?