Boost phase may be when a missile is most vulnerable but the intercept near impossible to do unless you have the interceptors within at least 100km of the boosting missile and positioned in the ideal places and in the direction of missile travel. Against North Korea this is entirely possible with AEGIS destroyers and cruisers positioned near launch.
Airborne lasers simply don't work because you're flying a big slow plane well within 1000km of launching missile. Until lasers become much more powerful and offer proper stand off range, the concept isn't effective. I really doubt any airborne laser system in the future can even get close to 1000km effective burning range against hardened missile. Even if these concepts become minimally effective in the future, it'll still take maybe even a minute to burn through a hardened target at 1000km or so. Right now, ship based (and powered) lasers can barely fry soft composites and plastics at 30km out within 20 seconds per target.
The only perfect counter to missiles is a sort of wonderweapon electronic attack like a strong EMP. Directing a strong enough EMP to a region the size of even India is near impossible for now ... oh and directing it from a distance and using "magic" aka yet undiscovered or unexploited new discoveries in physics and possible geophysics (to take advantage of geophysics since that would be the only way).
Oh and lasers don't work against ballistic missiles because ballistic missiles deal with immense surface heating already and far more than a laser can throw at any reasonable distance. It doesn't take much to make missiles of those sizes totally resistant to whatever an ABL can throw even the entire course of boost phase. Throwing photos on a surface is one thing, burning it is billions of times more demanding.
As said before, China reaching nuclear parity and beyond "minimal deterrence" not only includes updating delivery like we've seen but also increasing warhead numbers, warhead yields, and the numbers of delivery systems. Better ways of hiding and launching them e.g. world leading SSBN levels (and lots of them) and underground launch facilities. Chinese leaders know the US plays the henchman role and its population only complicit (many not even aware they are or that they are totally brainwashed) in perpetuating the sort of violent type of manifestation of this deeply rooted imperialism that controls most of Europe and north America. The mob boss isn't the US and in MAD, other targets must be hit so that's where the more missiles and more warheads come in.