Office 365 doesn't seem to be free, for anyone.
Windows Phone 8.x's Office apps gave the ability to edit, without a subscription.
The old Windows 10 Office apps did the same.
The new Windows 10 Office Mobile apps only allow viewing, for free.
Editing requires an Office 365 subscription.
It's a pain in the butt that has removed all usefulness.
Interestingly enough, the OneNote app still allows editing.
Apparently, it's considered it's own app.
Thankfully, an Office 365 subscription isn't required to edit on office.com.
Hopefully, that doesn't change too.
JJ