Although phragmites is a very invasive weed, it does provide great bedding cover. Deer prefer to bed in habitat similar to phragmites. I doubt by hinge cutting some trees, you will change where deer bed in your area. If the phragmites are controlled (by using specific herbicides), the deer might rapidly adapt to the next most suitable bedding cover. On the other hand, if closed-canopy forest was the only cover type within the home range of those deer, they would readily adapt to using the hinged cut trees for cover.
If you do opt to hinge cut for the purpose of developing ground-level cover, you should burn first, then hinge cut. The timing of fire is more important than the timing of hinge-cutting most trees. Please always use caution when using prescribed fire!
Growing Deer together,