With more sphag on there it won't need higher humidity.
A single layer of sphag will dry quickly no matter how large the area covered is.
Mine has about an inch or more of sphag extending beyond the base of the plant. A bit thicker layer towards the center.
During the warm, dry daytime weather we have, I water well in the morning - it's dry by night. During hot, very dry days, it may get watered twice. Our daytime humidity during much of the year is usually around 25%, often lower. When it really heats up, under 20%, sometimes under 10% - so VERY dry days - but it goes up a lot at night (with much cooler temps).
You can leave the old sphag and the staples - just add more sphag - you can use plant twist tie, velcro tape, yarn (synthetic) or other material that won't disintegrate, and isn't too difficult to handle for you, to secure the added sphag.
I took some pix of mine, but it's dark, and I don't have a proper camera (no flash), so I hope you can see them ok ...
I've not had mine very long - got the plant and mounted it in March - but it has been doing well so far. I have a skewer in the moss, to help me judge when it's thoroughly dry
If your Phrag gets moderately bright light or more, the Enc. may be fine hanging out with it

I don't grow any Phrags, so don't know how much light they take...
