4" toilet flange / basement bath

In the image is a 4" toilet flange on top of a 4" 90 sweep. (new basement bathroom)

I need to cement the floor to make it level. My concern is that I will need to raise the toilet flange.
What type of fitting is needed to do this?

I would rather not raise ALL of the drain pipe in order for the flange to be level with the floor.

The flange is not glued in.

Should I just remove the flange and add six more inches of PVC, and then when I am ready to add the flange (after the floor has been laid) just cut off the pvc as necessary? If so, I guess I'll find a flange that fits inside the diameter of a 4" pvc pipe.

Am I approaching this the right way?

If your slab will be thick enough to have enough sticking up without the coupler getting in the way, that would be one way. If you want to retain the use of an external mount flange, you can put some foam or cardboard around the pipe so you can dig it out after pouring the slab. The flange is designed to sit on TOP of the FINSIHED floor. So, depending on whether that eventually becomes sheet goods, or tile, having the stub sticking up so you can later install the flange is the better way to go. On a 4" pipe, you do have th eoption of an internal mount flange, then you can pour the concrete right up to the pipe, cut it off once the finished floor is in, then install the flange. BTW, consider a flange with a SS ring...the all plastic ones can distort or break over time with the bolts that hold the toilet to it.