Rhododendron flower buds are very distinctive - large and shaped like a tight pine cone or the dome of a Russian Orthodox church. (Azalea buds are similar, but usually smaller) Deer absolutely love them, so that may be your problem. Notched leaves usually indicate damage from vine weevils, but may also be from deer.

Lots of high winds with low temperatures last winter in the northeast led to a great deal of winterburn. Nova Zembla is rated as very hardy, but in my experience suffers from windburn more than many other varieties.

Gibraltar is a deciduous azalea so loses its leaves each fall even though it sets flower buds at that time. If you see evidence of deer eating them, that's the most likely reason the buds have been lost.

Phosphorous is unlikely to do any good unless a soil test shows a need. A light application of Hollytone or another complete fertilizer made for acid loving plants may help the plants grow.

The number one reason for problems with rhododendrons is failure to loosen the rootball when planting and/or failing to make sure the rootball is sufficiently damp. If you put them directly into the ground without doing these things, it's easy enough to dig them up and replant. There are spray products which allegedly (I'm pretty much a skeptic when it comes to hungry deer) protect plants from them.