What special materials other than pulse phasers? Everything else is the same. The hull would be stronger and ablative armor would be installed as well so more is needed for this area.
The Defiant was a test bed for new technology, so we can't say 'Everything else is the same'. A lot of the systems would be brand new, revolutionary, so would have to be manufactured specially. Until such time as dedicated manufacturing systems can be set up, this would be a small scale operation, and comparatively slow.
Ablative armour has shown itself to be very useful on occasions, yet isn't standard across the fleet. This suggests (though does not prove) that it is in limited supply for some reason. The most likely explanation, though others exist, is that such armour requires uncommon materials to manufacture.
It requires nothing of the sort.
Ablative armor is another of those REAL TECHNOLOGY concepts which were adopted into "Treknology."
Ablative armor, simply put, is armor which is designed to dissipate energy by being burned off, rather than allowing that energy to penetrate.
We use ablative armor today, in many different applications.
The problem with this sort of armor is that (1) it has to be replaced after use, and (2) it adds a lot of weight to the object it's attached to.
(This is similar in concept to, but not identical to, something we also use currently called "reactive armor"... but while ablative armor simply burns off, reactive armor is typically made from an actual explosive compound, to "decentralize" the energy from any weapon impact.)
In other words... the reason that most ships don't carry ablative armor is because of the mass penalty associated with the technology, not the complexity of the technology.
The Defiant, on the other hand, has "oversized engines" and so forth... with tiny little "closet-like" cabins, no science facilities, and a medical bay smaller than my kitchen. Those "oversized engines" provide propulsion for the weapons and defensive systems, with very little in the way of accommodation for crew.
One of those defensive systems is "ablative armor." Presumably, the Defiant has a "resource replenishment" bay someplace, where they can draw material from in order to use a replication scheme to repair burned-away armor plating in between engagements.
The mass of such armor is not inconsiderable, even for a ship like Defiant... but it would totally undermine the mission profile of a ship like a Galaxy.
Again... the technology isn't expensive, or hard to implement... it's just very, very heavy.
For modern-day equivalents... think of the reentry heat shields from the Apollo-program space capsules.