Re: No flange. Can we use toilet?
Personally I wouldn't leave it like this and frankly surprised the plumber did.
Didn't the plumber show and explain to you how the flange works?
The flange provides a proper transition to the drain pipe. It has a slight bevel and fits in to funnel the waste directly into the drain pipe. As well this allows the wax ring to act as a gasket to seal from moisture and sewer gas leaks. Along with the exit port of the toilet to properly fit in place instead of relying on you hopefully have it aligned with the raw opening of the drain pipe.
Just a thought.
"" an ounce of perception -- a pound of obscure "